Liquid ejection apparatus

In a liquid ejection apparatus, a controller of the liquid ejection apparatus is configured to, in response to receiving a recording instruction to instruct the liquid ejection apparatus to perform image recording on a recording medium, perform ejection inspection to determine whether liquid is ejected from each nozzle of a liquid ejection head toward an electrode based on a signal outputted from a signal output circuit. For the ejection inspection, the controller is configured to control a voltage applying circuit to apply an inspection voltage between the electrode and the liquid ejection head. In response to detecting that a leakage current greater than a predetermined value flows between the electrode and the liquid ejection head, the controller is configured to cancel the ejection inspection and control a voltage applying circuit to apply a reverse voltage opposite in polarity to the inspection voltage between the electrode and the liquid ejection head.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from Japanese Patent Application No. 2020-056011 filed on Mar. 26, 2020, the content of which is incorporated herein by reference in its entirety.

BACKGROUND

Examples of a liquid ejection apparatus that ejects liquid from nozzles include an inkjet recording apparatus that ejects ink from nozzles. A known inkjet recording apparatus includes a capping member having an opening edge defining an opening. The capping member is to cover the nozzles with the opening edge in contact a surface having the nozzles (e.g., a nozzle plate). The capping member accommodates an electrode. Inspection of whether ink is ejected from the nozzles is performed with the opening edge of the capping member spaced from the nozzle plate of a print head. In the inspection, the print head is moved to eject ink from the nozzles toward the electrode to which voltage is applied (or toward an inspection area). This prevents deposits of ink accumulating in the inspection area from contacting the nozzle plate, lowering the possibility that a leakage current flows between the electrode and the print head.

SUMMARY

According to one or more aspects of the disclosure, a liquid ejection apparatus includes a liquid ejection head having an array of nozzles, a cap configured to cover the nozzles, an electrode accommodated in the cap, a voltage applying circuit, a signal output circuit connected to the electrode, and a controller. The liquid ejection head is configured to eject liquid from each of the nozzles. The voltage applying circuit configured to apply a voltage between the electrode and the liquid ejection head. The controller is configured to, in response to receiving a recording instruction to instruct the liquid ejection apparatus to perform image recording on a recording medium, perform ejection inspection to determine whether liquid is ejected from each nozzle toward the electrode based on a signal outputted from the signal output circuit. To perform the ejection inspection, the controller is configured to cause the liquid ejection head and the cap to face each other, control the voltage applying circuit to apply an inspection voltage between the electrode and the liquid ejection head with the liquid ejection head and the cap facing each other, and drive the liquid ejection head to eject liquid from a nozzle of the nozzles toward the electrode. During the ejection inspection, the controller is configured to detect whether a leakage current greater than a predetermined value flows between the electrode and the liquid ejection head based on a signal from the signal output circuit. In response to detecting that a leakage current greater than the predetermined value flows between the electrode and the liquid ejection head, the controller is configured to cancel the ejection inspection and control the voltage applying circuit to apply a reverse voltage opposite in polarity to the inspection voltage between the electrode and the liquid ejection head.

According to the one or more aspects of the disclosure, if a leakage current greater than the predetermined value flows between the electrode and the liquid ejection head during ejection inspection, the ejection inspection is suspended, and a reverse voltage opposite in polarity to the inspection voltage is applied therebetween. The electric charge accumulated in the inkjet head can be thus discharged therefrom in response to the leakage current flowing. This enables the ejection inspection under a state that the nozzles are brought as close to the cap as possible.

DETAILED DESCRIPTION

In the above-described known inkjet recording apparatus, during the nozzle inspection, the capping member and the nozzle plate are spaced to prevent a leakage current from flowing. However, a small distance between the capping member and the nozzle plate may cause a leakage current to flow via ink adhering to the opening edge of the capping member and other objects. In contrast, a large distance between the capping member and the nozzle plate may reduce the strength of a signal to be outputted when ink is ejected from a nozzle toward the electrode for inspection.

Aspects of the disclosure provide a liquid ejection apparatus configured to output a signal with adequate strength when ink is ejected from a nozzle of a liquid ejection head toward an electrode in a cap to which voltage is applied, based on the presumption that a leakage current flows between the liquid ejection head and the electrode.

Hereinafter, an illustrative embodiment will be described with reference to the accompanying drawings.

General Configuration of Printer

As illustrated inFIG. 1, a printer1(as an example of a liquid ejection apparatus) includes a carriage2, a subtank3, an inkjet head4(as an example of a liquid ejection head), a platen5, conveyance rollers6and7, and a maintenance unit8.

The carriage2is supported by two guide rails11and12each extending in a scanning direction (e.g., a right-left direction). The carriage2is configured to reciprocate in the scanning direction along the guide rails11and12. The carriage2is connected to a carriage motor86(inFIG. 6) via a belt. In response to driving of the carriage motor86, the carriage2moves in the scanning direction along the guide rails11and12. The scanning direction corresponds to a right-left direction as illustrated inFIG. 1.

The subtank3is mounted on the carriage2. The printer1further includes a cartridge holder13. The cartridge holder13accommodates a plurality of, for example, four, ink cartridges14that are detachable. The four ink cartridges14arranged in the scanning direction store ink (as an example of liquid) of different colors, from right to left, black, yellow, cyan, and magenta, respectively. The subtank3is connected via four tubes15to the four ink cartridges14attached to the cartridge holder13. Such a configuration thus enables supply of ink of the four colors to the subtank3from the four ink cartridges14. The cartridge holder13includes cartridge sensors16(inFIG. 6) for the respective ink cartridges14. The cartridge sensors16are each configured to output a signal corresponding to whether a corresponding ink cartridge14is attached to the cartridge holder13.

The inkjet head4is mounted on the carriage2and connected to a lower end of the subtank3. The inkjet head4is supplied with ink of the four colors from the subtank3.

The inkjet head4has an array of nozzles10defined in a nozzle surface4athat is its lower surface. The inkjet head4is configured to eject ink from the nozzles10. Specifically, for example, the nozzles10are arranged in rows extending in a conveyance direction orthogonal to the scanning direction to form nozzle rows9. The inkjet head4includes a plurality of, for example, four, nozzle rows9next to each other in the scanning direction. In the inkjet head4, black ink is ejected from the nozzles10constituting the rightmost nozzle row9in the scanning direction. Yellow ink is ejected from the nozzles10constituting the nozzle row9to the left of the black nozzle row9. Cyan ink is ejected from the nozzles10constituting the nozzle row9to the left of the yellow nozzle row9. Magenta ink is ejected from the nozzles10constituting the nozzle row9to the left of the cyan nozzle row9.

The platen5is disposed below the inkjet head4and faces the nozzles10. The platen5extends in the scanning direction to have a dimension covering the entire width of a recording sheet P (as an example of a recording medium) to be conveyed. The platen5is configured to support from below a recording sheet P being conveyed. The conveyance roller6is disposed upstream of the inkjet head4and the platen5in the conveyance direction. The conveyance roller7is disposed downstream of the inkjet head4and the platen5in the conveyance direction. The conveyance rollers6and7are connected to a conveyance motor87(inFIG. 6) via gears. In response to driving of the conveyance motor87, the conveyance rollers6and7rotate to convey a recording sheet P in the conveyance direction.

The maintenance unit8includes a cap71, a suction pump72, a waste liquid tank73, and a wiper56. The cap71is disposed to the right of the platen5in the scanning direction. The cap71has a rectangular planar shape. The cap71has a lip portion71aprotruding upward or toward the inkjet head4around an outer edge of the cap71. When the carriage2is located in a maintenance position, the nozzles10face the cap71. The maintenance position is further to the right than the platen5in the scanning direction.

The cap71is movable upward and downward selectively by control of a cap up-and-down mechanism88(inFIG. 6). The carriage2is moved to stop at the maintenance position so that the nozzles10and the cap71face each other. In such a state, in response to the cap71being moved upward by the cap up-and-down mechanism88, the lip portion71aof the cap71intimately contacts the nozzle surface4aof the inkjet head4to cover the nozzles10. At this time, the cap71that covers the nozzles10is in a capping state, and the nozzles10capped by the cap71are in a capped state. The cap71is not limited to have such a configuration that the lip portion71aintimately contacts the nozzle surface4ato cover the nozzles10. The cap71may be structured such that that the lip portion71aintimately contacts a frame surrounding the nozzle surface4aof the inkjet head4to cover the nozzles10.

The suction pump72may be a tube pump. The suction pump72is connected to the cap71and the waste liquid tank73. The maintenance unit8use the suction pump72to perform suction purge in which, in response to driving of the suction pump72in a state where the nozzles10are in the capped state, ink in the inkjet head4is pumped out or discharged from the nozzles10. The suction purge is an example of a discharging operation. Ink discharged from the inkjet head4by the suction purge is collected in the waste liquid tank73.

For the sake of convenience, in this embodiment, the cap71covers all the nozzles10of the inkjet head4and the suction purge is performed to discharge ink in the inkjet head4from all the nozzles10. In some embodiments, the maintenance unit8may include a plurality of caps71, one for covering the nozzles10constituting the rightmost nozzle row9from which black ink is discharged, and the other for covering the nozzles10constituting the remaining three nozzle rows9from which respective color inks (e.g., yellow, cyan, and magenta inks) are discharged. Such a configuration may enable the suction purge to discharge black ink or color inks selectively in the inkjet head4. Alternatively, for example, the maintenance unit8may include a plurality of caps71for respective nozzle rows9. Such a configuration may enable ink to be discharged from the nozzles10of the inkjet head4on a nozzle row9basis.

As illustrated inFIG. 2, a detection electrode91having a rectangular planar shape is disposed within the cap71. The detection electrode91is connected to a high-voltage power supply circuit92(as an example of a voltage applying circuit) via a resistor93. The high-voltage power supply circuit92is connected to a conductive portion of the inkjet head4. The conductive portion is defined by plates32to35of the inkjet head4that are made of a conductive material. The conductive portion of the inkjet head4is connected to a ground terminal of the high-voltage power supply circuit92, and maintained at ground potential. The detection electrode91receives an electric potential or a voltage from the high-voltage power supply circuit92. Thus, the high-voltage power supply circuit92applies voltage between the detection electrode91and the conductive portion of the inkjet head4.

The detection electrode91is connected to a signal output circuit94. The signal output circuit94includes a filter circuit95and an amplifier circuit96. The filter circuit95is connected to the detection electrode91. The filter circuit95has a capacitor95aand a resistor95b, and removes a high-voltage DC component from the potential of the detection electrode91applied by the high-voltage power supply circuit92. A signal corresponding to which the filter circuit95has removed the high-voltage DC component from the potential of the detection electrode91is outputted from an output94aof the signal output circuit94.

The filter circuit95is connected to the amplifier circuit96. The amplifier circuit96amplifies the signal of which the filter circuit95has removed the high-voltage DC component from the potential of the detection electrode91. The signal amplified by the amplifier circuit96is outputted from an output94bof the signal output circuit94.

In an ejection inspection described later in this embodiment, the high-voltage power supply circuit92applies the inspection voltage (e.g., approximately 300 v) between the detection electrode91and the conductive portion of the inkjet head4by maintaining the conductive portion at the ground potential, applying a predetermined positive potential (e.g., approximately 300 v) to the detection electrode91, and setting the nozzles10in the capped state, in order to drive the inkjet head4to eject ink droplets from the nozzles10in the capped state.

In a case where ink is ejected from a nozzle10, ink becomes electrically charged by the potential difference between the detection electrode91and the conductive portion of the inkjet head4. Until the charged ink approaches and reaches the detection electrode91, the potential of the detection electrode91rises from a potential at which the inkjet head4is not driven. After the charged ink reaches the detection electrode91, the potential of the detection electrode91gradually lowers to the potential thereof at which the inkjet head4is not driven. In other words, the potential of the detection electrode91changes in a driving period Td during which the inkjet head4is driven.

However, the change in the potential of the detection electrode91is not so large at this time. As described above, the signal output circuit94is structured such that the potential of the detection electrode91from which the high-voltage DC component has been removed at the filter circuit95is amplified at the amplifier circuit96and then outputted from the output94b. As illustrated inFIG. 3A, in the driving period Td of the inkjet head4, the potential outputted from the output94brises from a potential V1at which the inkjet head4is not driven, reaches a potential V2, which is higher than the potential V1, and gradually lowers to the potential V1.

In contrast, in a case where ink is not ejected from a nozzle10while the inkjet head4is driven, the potential of the detection electrode91hardly changes from the potential at which the inkjet head4is not driven in the driving period Td of the inkjet head4. Thus, as illustrated inFIG. 3B, the potential outputted from the output94bhardly changes from the potential V1in the driving period Td of the inkjet head4.

The signal output circuit94thus outputs, from the output94b, a signal responsive to whether a nozzle10is a failure nozzle that does not eject ink. As illustrated inFIG. 3A, a threshold value Vt satisfying an equation V1<Vt<V2is specified to determine whether a nozzle10is a failure nozzle based on whether a maximum potential outputted from the output94bexceeds the threshold value Vt in the driving period Td of the inkjet head4.

As described above, when the high-voltage power supply circuit92applies the inspection voltage for between the detection electrode91and the conductive portion of the inkjet head4and the inkjet head4is driven to eject ink from the nozzles10in the capped state, a leakage current greater than a predetermined value may flow between the detection electrode91and the inkjet head4, for example, via ink adhering to the lip portion71aof the cap71. In the following, “a leakage current greater than a predetermined value flows” may refer to “a leakage occurs”.

When a leakage occurs, the potential of the detection electrode91changes. The change in the potential of the detection electrode91is much larger at the leakage than at which ink is ejected from the nozzle10to the detection electrode91.

Thus, the signal output circuit94is structured such that the potential of the detection electrode91from which the high-voltage DC component has been removed at the filter circuit95is outputted from the output94awithout being amplified at the amplifier circuit96. The signal output circuit94thus outputs, from the output94a, a signal responsive to whether a leakage has occurred. The value of the signal varies responsively to the magnitude of the leakage current.

In this embodiment, the high-voltage power supply circuit92applies the inspection voltage between the detection electrode91and the conductive portion of the inkjet head4by maintaining the conductive portion at the ground potential and applying the predetermined positive potential to the detection electrode91. However, the high-voltage power supply circuit92may apply an inspection voltage between the detection electrode91and the conductive portion of the inkjet head4by maintaining the conductive portion at the ground potential and applying a predetermined negative potential (e.g., approximately −300 v) to the detection electrode91. In this case, the rising and dropping of the potential outputted from the outputs94aand94bbecomes opposite to that described above.

Alternatively, the high-voltage power supply circuit92may apply an inspection voltage between the detection electrode91and the conductive portion of the inkjet head4by applying a potential other than the ground potential to the conductive portion and applying a different potential to the detection electrode91. In this case, when the high-voltage power supply circuit92applies, to the detection electrode91, a potential higher than that of the conductive portion of the inkjet head4, the rising and dropping of the potential of the detection electrode91at which ink is ejected from the nozzle10becomes similar to that illustrated inFIG. 3A. When the high-voltage power supply circuit92applies, to the detection electrode91, a potential lower than that of the conductive portion of the inkjet head4, the rising and dropping of the potential of the detection electrode91at which ink is ejected from the nozzle10becomes opposite to that illustrated inFIG. 3A.

The wiper56is located between the platen5and the cap71in the scanning direction. The wiper56includes a wiper blade57and a support member58. The wiper blade57is made of an elastic material such as rubber, and is a thin plate-shaped member extending in the vertical direction and in the conveyance direction. The support member58supports a lower end of the wiper blade57.

The support member58is movable upward and downward together with the wiper blade57by control of a wiper up-and-down mechanism59. When the support member58is lowered by the wiper up-and-down mechanism59, an upper end of the wiper blade57is located below the nozzle face4a. When the support member58is raised by the wiper up-and-down mechanism59, the upper end of the wiper blade57is located above the nozzle face4a. In a case where the wiper56is kept raised, the carriage2is moved in the scanning direction in a region where the nozzle face4aand the wiper56face each other. During the movement of the carriage2, the nozzle surface4aand the wiper blade57move relative to each other in the scanning direction while the wiper blade57contacts the nozzle surface4awith the upper end of the wiper blade57being elastically deformed. This is wiping in which the wiper blade57wipes ink adhering to the nozzle surface4a.

The wiper56is not limited to the above configuration of wiping ink adhering to the nozzle surface4aby the wiper blade57that is thin plate shaped. For example, a wiping member wound around a roller as disclosed in Japanese Patent No. 5899840 may be used. During the movement of the carriage2, the nozzle surface4aand the wiping member may relatively move in contact with each other such that the wiping member can wipe ink adhering to the nozzle surface4a.

Inkjet Head

A detailed configuration of the inkjet head4will be described. As illustrated inFIGS. 4, 5A, and 5B, the inkjet head4has a channel unit21and a piezoelectric actuator22.

The channel unit21includes a plurality of, for example, five plates31,32,33,34, and35stacked on one above another in this order from below in the vertical direction. The plate31is made of a synthetic resin material. The plates32to35are made of a conductive material such as metal. The stacked plates31to35are bonded, for example, by a thermosetting adhesive.

The channel unit21includes a plurality of individual channels41and four common channels42. As with the nozzles10arranged in the four nozzle rows9as described above, the individual channels41are arranged in four individual-channel rows29each extending in the conveyance direction. The channel unit21has the four individual-channel rows29next to each other in the scanning direction.

Each individual channel41includes a nozzle10, a pressure chamber51, a descending channel52, and a narrowed channel53. The pressure chamber51has a left end in the scanning direction connected to the nozzle10via the descending channel52, and a right end connected to the narrowed channel53. The nozzle10, the pressure chamber51, the descending channel52, and the narrowed channel53are similar in structure and positional relationship to those known in the art. Thus, further detailed description thereof will be omitted.

The four common channels42correspond to the four individual-channel rows29. Each common channel42extends in the conveyance direction, and overlaps right portions of individual channels41in a corresponding individual-channel row29in the vertical direction. Each common channel42is connected to right ends of the narrowed channels53constituting the individual channels41. Each common channel42has a supply port42aat its upstream end in the conveyance direction. Ink is to be supplied from the supply port42a.

The piezoelectric actuator22has a vibrating plate61, a piezoelectric layer62, a common electrode63, and a plurality of individual electrodes64. The vibrating plate61is made of a piezoelectric material having, as a main ingredient, lead zirconate titanate, which is a mixed crystal of lead titanate and lead zirconate. The vibrating plate61is disposed on an upper surface of the channel unit21(i.e., an upper surface of the plate35) and covers the pressure chambers51. The piezoelectric layer62is made of the piezoelectric material described above. The piezoelectric layer62is disposed on an upper surface of the vibrating plate61and extends continuously over the pressure chambers51. In this embodiment, the vibrating plate61and the piezoelectric layer62are made of the piezoelectric material. The vibrating plate61, however, may be made of an insulating material other than a piezoelectric material, for example, a synthetic resin material.

The common electrode63is disposed between the vibrating plate61and the piezoelectric layer62, and extends over their entire surfaces. The common electrode63is connected to a power supply via a wire and maintained at the ground potential. The individual electrodes64are disposed on an upper surface of the piezoelectric layer62. Each individual electrode64is provided for a corresponding pressure chamber51and vertically overlaps a central portion of the corresponding pressure chamber51in the vertical direction. Each individual electrode64is connected to a driver IC89(inFIG. 6) via a corresponding wire. Each individual electrode64receives the ground potential or a predetermined drive potential (e.g., approximately 20 v) selectively from the driver IC89. As the common electrode63and the individual electrodes64are disposed as described above, the piezoelectric layer62is polarized at portions sandwiched between the common electrode63and the individual electrodes64in its thickness direction.

The piezoelectric actuator22changes a potential difference between the common electrode63and each individual electrode64carrying a potential supplied from the driver IC89to deform the piezoelectric layer62and portions of the vibrating plate61overlapping with the pressure chambers51in the vertical direction. This fluctuates ink pressure in the pressure chambers51, thus enabling the nozzles10communicating with the pressure chambers51to eject ink.

Electrical Configuration of Printer

Hereinafter, a description will be provided on an electrical configuration of the printer1. As illustrated inFIG. 6, the printer1includes a controller80that controls operation of the printer1. The controller80includes a CPU81, a ROM82, a RAM83, a flash memory84, and an ASIC85. The controller80controls the carriage motor86, the driver IC89, the conveyance motor87, the cap up-and-down mechanism88, the suction pump72, the high-voltage power supply circuit92, and the wiper up-and-down mechanism59. In this embodiment, the controller80controls the inkjet head4by controlling the driver IC89.

The controller80receives a signal responsive to whether a nozzle is a failure nozzle, from the output94bof the signal output circuit94. The controller80receives a signal responsive to whether a leakage has occurred, from the output94aof the signal output circuit94. The controller80receives a signal responsive to whether the ink cartridges14are attached to the cartridge holder13, from the cartridge sensors16.

The printer1includes a display69, an operation device70, and a temperature sensor68. The display69may include a liquid crystal display. The controller80controls the display69to display information and messages related to the operations of the printer1. The operation device70includes buttons provided on the printer1and a touch screen provided on the display69. In response to the user operating the operation device70, the controller80receives a signal responsive to the operation. The temperature sensor68is used for detecting a temperature of the printer1. The controller80receives a signal corresponding to the detected temperature from the temperature sensor68.

In the controller80, only the CPU81or the ASIC85may perform all processing or a combination of the CPU81and the ASIC85may perform all processing. Alternatively, the controller80may include a single CPU81that may perform all processing or include a plurality of CPUs81that may share all processing. Alternatively, the controller80may include a single ASIC85that may perform all processing or include a plurality of ASICs85that may share all processing.

Control During Image Recording

Hereinafter, a description will be provided on a process of recording an image on a recording sheet P in the printer1. In the printer1, in response to receiving a recording instruction to instruct the printer1to perform image recording, the controller80executes processing in accordance with the flowchart ofFIG. 7.

More specifically, in response to receiving the recording instruction, the controller80starts ejection inspection (S101). In the ejection inspection, the controller80performs the following to determine whether the nozzles10include a failure nozzle. The controller80controls the carriage motor86and the cap up-and-down mechanism88to set the nozzles10in the capped state, and controls the high-voltage power supply circuit92to apply an inspection voltage between the detection electrode91and the inkjet head4. In this state, the controller80controls the driver IC89to drive the inkjet head4to eject ink from each nozzle10in sequence, and determines whether a nozzle10is a failure nozzle based on a signal outputted from the output94b.

If the controller80does not detect that a leakage occurs based on a signal from the output94a(S102: NO) and the ejection inspection is not finished (S103: NO), the controller80continues the ejection inspection. If the controller80does not detect that a leakage occurs (S102: NO) and the ejection inspection has been finished (S103: YES), the controller80determines whether the nozzles10of the inkjet head4include a failure nozzle (S104).

If the controller80determines that the nozzles10do not include a failure nozzle (S104: NO), the process proceeds to S107. If the controller80determines that the nozzles10include a failure nozzle (S104: YES), the controller80executes purging (S105). In purging in S105, the controller80controls the suction pump72to perform the suction purge described above. After purging in S105, the controller80resets a variable K to zero (S106) and proceeds to image recording in S107. The variable K corresponds to the number of occurrences of a leakage that the controller80has determined since previously performed purging. The variable K is set to zero at the time of manufacture of the printer1.

In image recording in S107, the controller80controls the conveyance motor87and a sheet feeder to convey a recording sheet P to the feeder and the conveyance rollers6and7. The controller80controls the carriage motor86to move the carriage2in the scanning direction, and controls the driver IC89to cause the inkjet head4to eject ink from the nozzles10, and controls the conveyance motor87to cause the conveyance rollers6and7to convey a recording sheet P for a predetermined distance. The controller80controls them repeatedly to record an image on the recording sheet P. After finishing recording the image on the recording sheet P, the controller80controls the conveyance motor87to cause the conveyance rollers6and7to discharge the recording sheet P. In a case where a recording instruction indicates image recording on two or more recording sheets P, the above operations are repeated until all recording sheets P have been printed.

In contrast, if the controller80detects that a leakage occurs before the ejection inspection is finished (S102: YES), the controller80suspends the ejection inspection (S108). At this time, the controller80controls the high-voltage power supply circuit92to terminate application of the inspection voltage. Subsequently, the controller80increments values of the variables K and M by one (109). The variable M corresponds to the number of occurrences of a leakage that the controller80has determined since a previous reverse voltage application, which will be described later. The variable M is set to zero at the time of manufacture of the printer1.

The controller80then determines whether an air trapped condition is satisfied (S110). The air trapped condition indicates that there is a high possibility that the inkjet head4has air trapped in its channels. The controller80determines that the air trapped condition is satisfied upon satisfaction of one of the following conditions that: for example, a purging instruction signal to perform suction purge has been input in response to the user operation of the operation device70; the printer1is not turned on for more than a certain time period; it is at a time immediately after the ink cartridges14are attached to the cartridge holder13; and the temperature is higher than a predetermined temperature.

In the above example, the purging instruction signal inputted to the controller80by a user operation on the operation device70, a power-on signal inputted to the controller80when the printer1is turned on after a certain length of time, a signal inputted to the controller80from the cartridge sensor16when an ink cartridge15is attached to the cartridge holder13, and a signal inputted to the controller80from the temperature sensor68are an example of items of information related to whether air is trapped in a liquid channel.

Where the air trapped condition is not satisfied (S110: NO), the controller80determines whether the variable M is below a predetermined value Mt. In response to determining that the variable M is below the predetermined value Mt (S111: YES), the controller80resumes the ejection inspection suspended in S108(S112), and returns to S102. In this case, the ejection inspection is continued.

Where the air trapped condition is satisfied (S110: YES), the controller80proceeds to S113. Where the air trapped condition is not satisfied (S110: NO) and the variable M is not below the predetermine value Mt, that is, greater than or equal to the predetermined value Mt (S111: NO), the controller80proceeds to S113. In these cases, the ejection inspection suspended in S108is never resumed. The ejection inspection is canceled.

In S113, the controller80determines whether the variable K is below a predetermined value Kt. Where the variable K is below the predetermined value Kt (S113: YES), the controller80proceeds to S116. Where the variable K is not below the predetermine value Kt, that is, greater than or equal to the predetermined value Kt (S113: NO), the controller80performs purging similar to that in S105(S114), resets the variable K to zero (S115), and proceeds to S116.

In S116, the controller80determines whether the number N of recording sheets P included in the recording instruction is below a predetermined number Nt. In response to determining that the number N of recording sheets P is below the predetermined number Nt (S116: YES), the controller80performs image recording similar to that in S107(S117). Subsequently, the controller80performs the reverse voltage application (S118), resets the variable M to 0 (S119), and then performs wiping (S120). The reverse voltage application to be performed in S118will be described later in detail. In S120, the controller80performs wiping described above by controlling the carriage motor86and the wiper up-and-down mechanism59.

In contrast, in response to determining that the number N of recording sheets P included in the recording instruction is not below the predetermined number Nt, that is, greater than or equal to the predetermined number Nt (S116: NO), the controller80performs reverse voltage application similar to that in S118(S121), resets the variable M to zero (S122), and performs wiping similar to that in S120(S123). Subsequently, the controller80performs image recording similar to that in S117(S124).

Reverse Voltage Application

Next, the reverse voltage application in S118and S121will be described. In the reverse voltage application in S118and S121, the controller80performs processing in accordance with the flowchart ofFIG. 8. More specifically, the controller80controls the high-voltage power supply circuit92to apply a reverse voltage that is the same in magnitude as the inspection voltage but opposite in polarity between the detection electrode91and the inkjet head4(S201). The controller80maintains the application of the reverse voltage unless a time T1has elapsed from the start of the application of the reverse voltage (S202: NO). Where the time T1has elapsed from the start of the application of the reverse voltage (S202: YES), the controller80controls the high-voltage power supply circuit92to cancel the application of the reverse voltage (S203). The time T1refers to a time during which a leakage current greater than the predetermined value flows from the time at which the controller80detects that a leakage occurs in S102to the time at which the controller80suspends ejection inspection in S108and cancels the application of the inspection voltage. This time is measured by a timer built in the controller80.

Effects

In response to the occurrence of a leakage, ink is electrolyzed. This may cause hydrogen gas in the individual channels41, thereby increasing ink pressure. The electrolysis may change ink properties. The longer the time for which ink is electrolyzed, the more likely the above factors are to cause problems such as separation between the plate31and the plate32. Thus, ink may be electrolyzed in as short time as possible in response to the occurrence of a leakage.

Furthermore, the inkjet head4has capacitance. Electric charge accumulates in the inkjet head4on the occurrence of a leakage, and electrolysis of ink proceeds after electric charge has accumulated throughout the inkjet head4. The electric charge remaining in the inkjet head4after the leakage may accelerate the electrolysis of ink immediately after the next leakage occurs. As a result, ink may be electrolyzed in a longer time.

In this embodiment, however, if an occurrence of a leakage between the detection electrode91and the inkjet head4is detected during ejection inspection, the ejection inspection is suspended, and a reverse voltage opposite in polarity to the inspection voltage is applied therebetween. The electric charge accumulated in the inkjet head4can be thus discharged therefrom in response to the occurrence of a leakage.

The ejection inspection may be performed by bringing the nozzles10as close to the detection electrode91as possible to increase change in potential of the detection electrode91at which ink is ejected from the nozzles10. However, a leakage is more likely to occur as the nozzles10are brought closer to the detection electrode91. In this embodiment, in response to the occurrence of a leakage, the electric charge accumulated in the inkjet head4can be discharged through the application of the reverse voltage. This enables the ejection inspection under a state that the nozzles10in the capped state are brought as close to the detection electrode91as possible.

In this embodiment, a reverse voltage having the same magnitude as the inspection voltage is applied for the same length of time as the time T1during which a leakage current greater than the predetermined value flows. Flowing of a leakage current can discharge the electric charge from the inkjet head4, thus reducing excessive application of the reverse voltage that may cause accumulation of electric charge with the opposite polarity in the inkjet head4.

When a leakage occurs, a leakage current flows to electrolyze ink. Deposits of ink electrolyzed may accumulate around the nozzles10of the nozzle surface4a. In this state, the nozzles10may not eject ink normally. In this embodiment, wiping is performed after the reverse voltage application to remove deposits from the nozzle surface4a.

In this embodiment, in a case where the number of recording sheets P to be recorded at one time is small, the reverse voltage application takes more time than recording on the recording sheets P. Therefore, unlike this embodiment, if the reverse voltage is applied before recording on the recording sheets P, the user may easily recognize a time lag between the recording instruction and the completion of recording on the recording sheets P. In addition, the time required for recording on the recoding sheets P is shorter than the time required for the reverse voltage application. Thus, the time for which the inkjet head4is maintained with the electric charge accumulated is short even if the reverse voltage is applied after the completion of recording on the recording sheets P. In this embodiment, in a case where recording is performed for the number of the recording sheets P smaller than the predetermined number Nt, the reverse voltage is applied after the completion of recording on the recording sheets P.

In contrast, in a case where the number of recording sheets P to be recorded at one time is large, the reverse voltage application takes less time than recording on the recording sheets P. Therefore, when the reverse voltage is applied before recording on the recording sheets P, the user may hardly recognize a time lag between the recording instruction and the completion of recording on the recording sheets P. In addition, in a case where the number of recording sheets P to be recorded at one time is large, recording on all recording sheets P takes a long time. Thus, unlike this embodiment, if the reverse voltage is applied after the completion of recording on the recoding sheets, the inkjet head4will be remained with the electric charge accumulated for a long time. In this embodiment, in a case where recording is performed for the number of the recording sheets P larger than the predetermined number Nt, recording on the recording sheets P is performed after the completion of the reverse voltage application.

In this embodiment, deposits of ink to be produced through electrolysis in every occurrence of a leakage may accumulate in the nozzles10. More deposits of ink in the nozzles10may hinder the nozzles10to eject ink normally. Therefore, in this embodiment, suction purge is performed when the variable K corresponding to the number of occurrences of a leakage that the controller80has determined since previously performed suction purge is greater than or equal to the predetermined value Kt. This enables discharging of the deposits having accumulated in the nozzles10before the deposit accumulation reaches a maximum amount.

In a case where no air is trapped in the individual channels41, a leakage current evenly flows through ink in the channels of the inkjet head4when a leakage has occurred. Thus, the value of the leakage current flowing through each part of the respective individual channels41is small and the speed at which the electrolysis of ink progresses is slow. In contrast, in a case where air is trapped in the individual channels41, ink in the respective individual channels41is partitioned by air. In this case, when a leakage occurs, a leakage current flows locally in ink that is partitioned by air and closer to the nozzles10in the individual channels41. As a result, the value of the leakage current becomes large, and the speed at which the electrolysis of ink progresses becomes fast.

In this embodiment, in a case where the air trapped condition is satisfied, the ejection inspection is immediately canceled and a reverse voltage is applied. In contrast, in a case where the air trapped condition is not satisfied, the ejection inspection is resumed when the variable M, which corresponds to the number of occurrences of a leakage has occurred since the previous reverse voltage application, is below the predetermined value Mt. When the variable M is greater than or equal to the predetermined value Mt, the ejection inspection is canceled and a reverse voltage is applied.

Modifications

While the disclosure has been described in detail with reference to the specific embodiment thereof, this is merely an example, and various changes, arrangements and modifications may be applied therein without departing from the spirit and scope of the disclosure.

In the above embodiment, in a case where the air trapped condition is satisfied, the ejection inspection is canceled (and never resumed) and the reverse voltage application is performed. In contrast, in a case where the air trapped condition is not satisfied, the ejection inspection is canceled and the reverse voltage application is performed when the variable M, which corresponds to the number of occurrences of a leakage that the controller80has determined since the previous reverse voltage application, is greater than or equal to the predetermined value Mt.

In some embodiments, regardless of whether the air trapped condition is satisfied, the ejection inspection may be immediately canceled in response to the occurrence of a leakage, to perform the reverse voltage application. Alternatively, regardless of whether the air trapped condition is satisfied, the ejection inspection may be resumed while the variable M is below the predetermined value Mt, and be canceled immediately when the variable M is greater than or equal to the predetermined value Mt, to perform the reverse voltage application.

In the above embodiment, suction purge is performed when the variable K, which corresponds to the number of occurrences of a leakage that the controller80has determined since the previous suction purge, is greater than or equal to the predetermined value Kt. However, suction purge may be performed regardless of the number of occurrences of a leakage that the controller80has determined since the previous suction purge.

In the above embodiment, in a case where a leakage has occurred, the reverse voltage application is performed after image recording when the recording instruction indicates the number N of recording sheets P is below the predetermined number Nt, and the reverse voltage application is performed before image recording when the recording instruction indicates the number N is larger than the predetermined number Nt.

However, the reverse voltage application may be performed after image recording, regardless of the number N of recording sheets P. Alternatively, the reverse voltage application may be performed before image recording, regardless of the number N of recording sheets P.

In the above embodiment, wiping is performed after the reverse voltage application. However, wiping may not be performed after the reverse voltage application.

In the above embodiment, the reverse voltage application is performed by applying a reverse voltage having the same magnitude as the inspection voltage and the opposite polarity thereto between the inkjet head4and the detection electrode91for the same length of time as the time T1during which a leakage current greater than the predetermined value flows. However, the reverse voltage application is not limited to this.

In a first modification, the controller80performs the reverse voltage application in accordance with the flowchart ofFIG. 9A. More specifically, the controller80controls the high-voltage power supply circuit92to apply a reverse voltage that is smaller in magnitude than the inspection voltage and is opposite in polarity between the detection electrode91and the inkjet head4(S301). The controller80maintains the application of the reverse voltage unless a time T2, which is longer in length than the time T1, has elapsed from the start of the application of the reverse voltage (S302: NO). Where the time T2has elapsed from the start of the application of the reverse voltage (S302: YES), the controller80controls the high-voltage power supply circuit92to cancel the application of the reverse voltage (S303).

In a second modification, the controller80performs the reverse voltage application in accordance with the flowchart ofFIG. 9B. More specifically, the controller80controls the high-voltage power supply circuit92to apply a reverse voltage that is larger in magnitude than the inspection voltage and is opposite in polarity between the detection electrode91and the inkjet head4(S401). The controller80maintains the application of the reverse voltage unless a time T3, which is shorter in length than the time T1, has elapsed from the start of the application of the reverse voltage (S402: NO). Where the time T3has elapsed from the start of the application of the reverse voltage (S402: YES), the controller80controls the high-voltage power supply circuit92to cancel the application of the reverse voltage (S403).

Even in the first and second modifications, flowing of a leakage current can discharge the electric charge from the inkjet head4, thus reducing excessive application of the reverse voltage that may cause accumulation of electric discharge with the opposite polarity in the inkjet head4.

The above embodiment, the first modification, and the second modification show, but are not limited to, the application of the reverse voltage for a time determined based on the time T1measured by the timer. The time from when a leakage is detected in S102and the ejection inspection is suspended in S108to when the application of the inspection voltage is canceled falls normally within a certain period of time. For example, information on a particular time falling within the certain period of time may be stored in the flash memory84, and the time for applying the reverse voltage may be determined based on the stored information on the particular time.

In the reverse voltage application, the magnitude of the reverse voltage to be applied between the detection electrode91and the inkjet head4and the time for applying the reverse voltage are not limited to those described in the above embodiment, the first modification, and the second modification.

In the above embodiment, ink is discharged from the nozzles10of the inkjet head4by suction purge. However, the discharging operation is not limited to the suction purge. Instead of the suction purge, a booster pump, for example, may be used. The booster pump may be disposed in portions of the tubes15connecting the subtank3and the ink cartridges14. Alternatively, the printer may include the booster pump to be connected to an ink cartridge. The booster pump may be driven in a state where the nozzles10are covered by the cap71to increase the pressure of ink in the inkjet head4, thereby causing the inkjet head4to discharge ink from the nozzles10toward the cap71. The so-called pressurized purging may be performed. In this case, the booster pump is an example of discharging means.

Alternatively, both of suction by the suction pump72and pressurization by the booster pump may be performed. In this case, a combination of the suction pump72, the waste liquid tank73, and the booster pump is an example of discharging means.

Alternatively, flushing may be performed by driving the inkjet head4to discharge ink from the nozzles10. In this case, the inkjet head4also serves as discharging means.

In the above embodiment, the ejection inspection is performed to determine whether the nozzles10include a failure nozzle that does not eject ink. In a case where ink is ejected from a nozzle10in an unintended direction, the time for which the ejected ink reaches the detection electrode91is long and the potential of the detection electrode91changes gently compared to a case where ink is ejected from a nozzle in an intended direction. From this reason, the ejection inspection may be performed to determine whether the nozzles10include a failure nozzle that ejects ink in an unintended direction, based on a period of time from when the inkjet head4is driven to when the potential outputted from the output94bexceeds the threshold value Vt.

In the above embodiment, the ejection inspection is performed with the nozzles10in the capped state. However, the ejection inspection may be performed with the nozzle surface4aslightly spaced from the lip portion71aof the cap71.

In the above embodiment, the controller80determines whether a leakage has occurred based on a signal from the output94aof the signal output circuit94connected to the detection electrode91. However, the controller80may determine whether a leakage has occurred based on a signal outputted from, for example, a circuit connected to the conductive portion of the inkjet head4. In this case, the signal may be responsive to change in potential of the conductive portion.

The disclosure has been applied to a printer including a serial head that moves in the scanning direction together with a carriage. However, the disclosure may also be applied to a printer including, for example, a line head extending over the entire length of a recording sheet P in the scanning direction.

The disclosure has been applied to a printer that ejects ink from nozzles to record an image on a recording sheet P. However, the disclosure may also be applied to another printer that may record an image on a recording medium other than a recording sheet. Examples of the recording media include a T-shirt, a sheet for outdoor advertisement, a casing of a mobile terminal such as a smartphone, a cardboard, and a resin member. Further, the disclosure may also be applied to a liquid ejection apparatus that may eject liquid other than ink such as liquid resin or liquid metal.