Patent Application
20130120503
1. Field of the Invention
The present invention relates to a liquid ejection apparatus and a drive method for an inkjet head, and more particularly to driving technology for a piezoelectric device arranged in an inkjet head.
2. Description of the Related Art
As drive methods for inkjet heads in inkjet recording apparatuses, there are known a piezoelectric method and a thermal method. In the piezoelectric method, ink is ejected from a nozzle by using a mechanical distortion of a piezoelectric device. In the thermal method, ink is ejected from a nozzle by using a film boiling effect of ink stored in a liquid chamber connected to the nozzle. The piezoelectric method has a beneficial effect in that the ink ejection volume and ejection velocity can be controlled more readily than the thermal method.
The piezoelectric device used in the inkjet head needs to be constituted of a piezoelectric element made of material having a high piezoelectric coefficient (electrical-mechanical transducing coefficient). For example, known materials for the piezoelectric elements include lead titanate (PT), lead zirconate titanate (PZT), and PZT doped with magnesium, manganese, cobalt, iron, nickel, niobium, scandium, tantalum, bismuth, or the like. The piezoelectric element used in the inkjet head is applied with an electric field of about several kilovolts per centimeter, in order to generate the pressure required for the ejection of ink.
Here, it is known that piezoelectric elements have a large number of defects, such as small cracks or voids, and the like. When an electric field of high intensity is applied to a piezoelectric element containing lead under conditions where water (moisture) is present, large electric current flows through the lead compound in the defective portion and the peripheral area thereof, and the location where the large electric current occurs is destroyed by Joule heat and hence creates a larger defect.
By forming the piezoelectric element with a large thickness, it is possible to avoid the occurrence of large defects which pass through the element due to the breakage; however, it becomes necessary to apply an electric field of high intensity to the piezoelectric element in order to obtain a desired pressure applied to the liquid in the liquid chamber, and hence there are concerns about increase in the electric power consumption.
Japanese Patent Application Publication No. 2004-322605 discloses an inkjet recording apparatus which is provided with a dew point control unit so as to keep the dew point in the atmosphere around the piezoelectric element and the vicinity of the piezoelectric element lower than the dew point in the environment of the inkjet recording apparatus, and describes that it is thereby possible to achieve a thin thickness of the piezoelectric element while preventing the breakage of the piezoelectric element due to application of high voltage to the piezoelectric element. More specifically, the dew point control unit includes a compressor and an air drier, which dries air compressed by the computer and supplies the dried air to a casing in which the piezoelectric element is sealed. However, in this composition, when the supply of the dried air to the casing is stopped, moisture can flow back into the casing through an inlet of the dried air and an outlet of the overflowing air. Moreover, if the atmosphere around the piezoelectric element is of high humidity before starting the supply of the dried air, then there is a problem of breakage of the piezoelectric element occurring the moment a voltage is applied to the piezoelectric element.
The present invention has been contrived in view of these circumstances, an object thereof being to provide a liquid ejection apparatus and a drive method for an inkjet head which readily prevents a piezoelectric element from breaking when a voltage is applied to the piezoelectric element, while attaining a thin film thickness of the piezoelectric element.
In order to attain the aforementioned object, the present invention is directed to a liquid ejection apparatus, comprising: an inkjet head including: a nozzle which is configured to eject liquid; a pressure chamber which is connected to the nozzle and is configured to contain the liquid to be ejected from the nozzle; a piezoelectric element which is arranged on a wall of the pressure chamber on an outer side of the pressure chamber and is configured to apply pressure to the liquid contained in the pressure chamber; and a gas chamber which surrounds the piezoelectric element and a space peripheral to the piezoelectric element; a dry gas supply device which is configured to generate dry gas having a dew point of not higher than a dew point of an atmosphere around the inkjet head, the dry gas supply device being configured to start supply of the dry gas to the gas chamber before supply of electric power to the inkjet head is started, to continue the supply of the dry gas to the gas chamber while the supply of the electric power to the inkjet head is continued, and to halt the supply of the dry gas to the gas chamber after the supply of the electric power to the inkjet head is halted; a dry gas supply flow channel which has a first end and a second end, the first end of the dry gas supply flow channel being connected to the dry gas supply device, the second end of the dry gas supply flow channel being connected to the gas chamber; a dry gas supply flow channel opening and closing device which is arranged in the dry gas supply flow channel and is configured to switch between connection and disconnection of the dry gas supply device and the gas chamber; a gas return flow channel which has a first end and a second end, the first end of the gas return flow channel being connected to the gas chamber, the second end of the gas return flow channel being open to external air; a gas return flow channel opening and closing device which is arranged in the gas return flow channel and is configured to switch between connection and disconnection of the gas chamber and the external air; and an opening and closing control device which is configured to control the dry gas supply flow channel opening and closing device and the gas return flow channel opening and closing device, wherein while the dry gas supply device halts the supply of the dry gas to the gas chamber, the opening and closing control device controls the dry gas supply flow channel opening and closing device to close to disconnect the dry gas supply device and the gas chamber, and controls the gas return flow channel opening and closing device to close to disconnect the gas chamber and the external air.
According to this aspect of the present invention, in the liquid ejection apparatus which supplies the dry gas to the gas chamber in which the piezoelectric element is arranged in the inkjet head so as to lower the dew point of the periphery of the piezoelectric element to prevent deterioration due to application of voltage to the piezoelectric element, since the dry gas supply flow channel and the gas return flow channel connected to the gas chamber are closed while the supply of the dry gas is halted, the penetration of gas including moisture into the gas chamber during a halt in the supply of the dry gas is prevented.
Preferably, when a prescribed period of time has elapsed after the dry gas supply device starts generation of the dry gas, the opening and closing control device controls the dry gas supply flow channel opening and closing device to open to connect the dry gas supply device and the gas chamber to start the supply of the dry gas to the gas chamber.
According to this aspect of the present invention, penetration of gas of high humidity into the gas chamber is prevented before the supply of the dry gas to the gas chamber is introduced.
Preferably, the liquid ejection apparatus further includes: a drive voltage application device which is configured to apply a drive voltage to the piezoelectric element, wherein when a prescribed period of time has elapsed after the dry gas supply device starts the supply of the dry gas to the gas chamber, the drive voltage application device starts application of the drive voltage to the piezoelectric element.
According to this aspect of the present invention, even if the gas chamber is in a high humidity state before the dry gas is introduced, the gas chamber is changed to a prescribed low humidity state by the time that the drive voltage is applied to the piezoelectric element, and hence breakage of the piezoelectric element upon application of the drive voltage to the piezoelectric element is prevented.
Preferably, the liquid ejection apparatus further includes: a humidity measurement device which is configured to measure a humidity in the gas chamber, wherein when the humidity in the gas chamber measured by the humidity measurement device has become not higher than a threshold humidity, the drive voltage application device starts the application of the drive voltage to the piezoelectric element.
According to this aspect of the present invention, breakage of the piezoelectric element upon application of the drive voltage is reliably prevented by applying the drive voltage to the piezoelectric element after the humidity of the gas chamber has become not higher than the prescribed threshold humidity.
Preferably, the humidity measurement device includes a humidity sensor which is arranged on a downstream side of the dry gas supply device in a flow direction of the dry gas.
According to this aspect of the present invention, it is possible to ascertain the humidity of the gas chamber on the basis of the humidity of the gas returned from the gas chamber.
Preferably, the liquid ejection apparatus further includes a moisture absorbing member which is arranged in at least one of the gas chamber, the dry gas supply flow channel and the gas return flow channel.
According to this aspect of the present invention, even if moisture penetrates inside the gas chamber when the supply of the dry gas is halted, it is possible to remove this moisture.
Preferably, the liquid ejection apparatus further includes a relief valve which is arranged in the dry gas supply flow channel.
According to this aspect of the present invention, even if the pressure inside the gas chamber rises due to a blockage in the gas return flow channel, or the like, breakage of the gas chamber and the gas chamber supply flow channel is prevented by operation of the relief valve.
Preferably, the liquid ejection apparatus includes a plurality of the inkjet heads; and a dry gas distributary flow channel which connects the dry gas supply flow channel to the respective inkjet heads.
Preferably, the liquid ejection apparatus further includes a gas tributary flow channel which connects the respective inkjet heads to the gas return flow channel.
It is also preferable that the inkjet head includes a plurality of head modules; and the liquid ejection apparatus further comprises a dry gas distributary flow channel which connects the dry gas supply flow channel to the respective head modules.
Preferably, the liquid ejection apparatus further includes a gas tributary flow channel which connects the respective head modules to the gas return flow channel.
For example, each of the dry gas distributary flow channel and the gas tributary flow channel can be formed with a manifold or a joint.
Preferably, the liquid ejection apparatus further includes a moisture absorbing member which is arranged in at least one of the dry gas distributary flow channel and the gas tributary flow channel.
According to this aspect of the present invention, even if moisture penetrates inside the at least one of the dry gas distributary flow channel and the gas tributary flow channel when the supply of the dry gas is halted, it is possible to remove this moisture.
Preferably, the dry gas supply device includes: a compression device which is configured to compress gas; a filter which is configured to remove foreign matter from the compressed gas; and an air drier which is configured to remove water content from the compressed gas that has passed through the filter.
It is also possible that the filter is incorporated in the air drier.
It is also preferable that the dry gas supply device includes a filter type air drier; and the liquid ejection apparatus further comprises a regulator which is arranged between the filter type air drier and the inkjet head.
According to this aspect of the present invention, by adopting the filter type air drier, on/off control of the air drier becomes unnecessary.
Preferably, the liquid ejection apparatus further includes at least one of a flow volume sensor and a humidity sensor arranged on a downstream side of the filter type air drier in a flow direction of the dry gas.
According to this aspect of the present invention, it is possible to detect an abnormal state where the dry gas is not supplied from the air drier.
Preferably, the dry gas supply flow channel has been degreased.
According to this aspect of the present invention, the penetration of foreign material, such as dust, into the gas chamber is prevented.
Preferably, the second end of the gas return flow channel has a gas outlet configured to discharge the dry gas flowing out from the gas chamber, the gas outlet being arranged to exterior of a print unit in which the inkjet head is arranged.
According to this aspect of the present invention, condensation on the inkjet head (and in particular, the liquid ejection surface) due to the discharged gas from the gas chamber, and the effects of the flow of the discharged gas on the ejected liquid, are prevented.
Preferably, the dew point of the dry gas is not higher than 15° C.
According to this aspect of the present invention, since the interior of the gas chamber is kept in a low humidity state, a prescribed operating life of the piezoelectric element can be ensured.
Preferably, at least one of the dry gas supply flow channel opening and closing device and the gas return flow channel opening and closing device is a normally closed type control valve which is closed while being not supplied with electric power.
According to this aspect of the present invention, since at least one of the dry gas supply flow channel and the gas return flow channel are closed when the electric power to the at least one of the dry gas supply flow channel opening and closing device and the gas return flow channel opening and closing device is turned off, then outflow of the dry gas from the gas chamber and inflow of gas having high humidity into the gas chamber are prevented while the electric power is off.
Preferably, at least one of the dry gas supply flow channel opening and closing device and the gas return flow channel opening and closing device is a latch type control valve.
According to this aspect of the present invention, there is little effect of heat generation in the at least one of the dry gas supply flow channel opening and closing device and the gas return flow channel opening and closing device when the at least one of the dry gas supply flow channel opening and closing device and the gas return flow channel opening and closing device is open.
In order to attain the aforementioned object, the present invention is also directed to a drive method for an inkjet head which comprises: a nozzle which is configured to eject liquid; a pressure chamber which is connected to the nozzle and is configured to contain the liquid to be ejected from the nozzle; a piezoelectric element which is arranged on a wall of the pressure chamber on an outer side of the pressure chamber and is configured to apply pressure to the liquid contained in the pressure chamber; and a gas chamber which surrounds the piezoelectric element and a space peripheral to the piezoelectric element and is connected with a dry gas supply flow channel and a gas return flow channel, the dry gas supply flow channel having a first end connected to a dry gas supply device and a second end connected to the gas chamber, the gas return flow channel having a first end connected to the gas chamber and a second end open to external air, the method comprising: before starting supply of electric power to the inkjet head, starting supply of dry gas to the gas chamber from the dry gas supply device through the dry gas supply flow channel, the dry gas having a dew point of not higher than a dew point of an atmosphere around the inkjet head; continuing the supply of the dry gas to the gas chamber while the supply of the electric power to the inkjet head is continued; halting the supply of the dry gas to the gas chamber after the supply of the electric power to the inkjet head is halted; and while the supply of the dry gas to the gas chamber is halted, disconnecting the dry gas supply device and the gas chamber by closing a dry gas supply flow channel opening and closing device arranged in the dry gas supply flow channel, and disconnecting the gas chamber and the external air by closing a gas return flow channel opening and closing device arranged in the gas return flow channel.
It is also possible to include a humidity measurement step of measuring a humidity inside the gas chamber, a judgment step of judging whether or not there is an abnormality in the humidity of the gas chamber, and a reporting step of reporting when it is judged that there is an abnormality in the humidity of the gas chamber in the judgment step.
According to the present invention, in the liquid ejection apparatus which supplies the dry gas to the gas chamber in which the piezoelectric element is arranged in the inkjet head so as to lower the dew point of the periphery of the piezoelectric element to prevent deterioration due to application of voltage to the piezoelectric element, since the dry gas supply flow channel and the gas return flow channel connected to the gas chamber are closed while the supply of the dry gas is halted, the penetration of gas including moisture into the gas chamber during a halt in the supply of the dry gas is prevented.
The nature of this invention, as well as other objects and advantages thereof, will be explained in the following with reference to the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures and wherein:
The recording medium conveyance unit 14 includes: an endless conveyance belt 18, which has a plurality of suction holes (not shown) in a recording medium holding region where the recording medium 12 is held; conveyance rollers including a drive roller 20 and an idle roller 22, about which the conveyance belt 18 is wrapped; a chamber 24, which is arranged on a rear side of the conveyance belt 18 in the recording medium holding region (on the surface opposite to the recording medium holding surface where the recording medium 12 is held) and which is connected to the suction holes (not shown) that are arranged in the recording medium holding region; and a vacuum pump 26 configured to generate negative pressure in the chamber 24.
A pressing roller 30 configured to prevent the recording medium 12 from floating is arranged in a recording medium entrance 28, through which the recording medium 12 enters the inkjet recording apparatus 10, and another pressing roller 34 is arranged in a recording medium exit 32, through which the recording medium 12 is outputted.
The recording medium 12 having entered the inkjet recording apparatus 10 through the recording medium entrance 28 receives negative pressure through the suction holes of the endless conveyance belt 18 arranged in the recording medium holding region, and is thereby held by suction onto the recording medium holding region of the conveyance belt 18.
A temperature adjustment unit 36 configured to adjust the surface temperature of the recording medium 12 to a prescribed range is arranged on the conveyance path of the recording medium 12, in a stage prior to the print unit 17 (to the upstream side in terms of the recording medium conveyance direction). An image reading device (sensor) 38 configured to read an image recorded on the recording medium 12 is arranged in a stage after the print unit 17 (to the downstream side in terms of the recording medium conveyance direction).
The recording medium 12 having entered the inkjet recording apparatus 10 through the recording medium entrance 28 is held by suction on the recording medium holding region of the conveyance belt 18, is then subjected to the temperature adjustment processing by the temperature adjustment unit 36, and is then subjected to image recording carried out by the print unit 17.
As shown in
The print unit 17 is not limited to the mode described above. For example, it is also possible that the print unit 17 further includes inkjet heads 16LC and 16LM corresponding to inks of light cyan (LC) and light magenta (LM), respectively. Moreover, the arrangement order of the inkjet heads 16K, 16C, 16M and 16Y can be changed appropriately.
The recorded image (or a test pattern) is read out by the image reading device 38, and the recording medium 12 on which the image has been recorded is then outputted through the recording medium exit 32.
The inkjet recording apparatus 10 shown in
The “full width” in the recording medium 12 can be the full dimension of the recording medium 12 in a main scanning direction M, which is perpendicular to the conveyance direction of the recording medium 12 (i.e., a sub-scanning direction S). In a case of taking account of the margins, the “full width” can be set as the full dimension in the main scanning direction M, of the image formation region where an image is formed in the recording medium 12.
Image formation in the main scanning direction M is carried out by ejecting and depositing droplets of inks from the inkjet heads 16K′, 16C′, 16M′ and 16Y′ onto the recording medium 12 while moving the carriage 13A along a guide 13B in the main scanning direction M. When the image formation is completed in a particular region of the recording medium 12, the recording medium 12 is moved by a prescribed amount in the sub-scanning direction S, and the image formation is carried out in the next region. An image can be formed over the whole region of the recording medium 12 by repeating these operations.
In the present invention, it is possible to use the line heads shown in
The inkjet head 16 shown in
The pressure chamber 52 is connected to a common flow channel 58 through a supply port (supply restrictor) 54. The common flow channel 58 is connected through a flow channel, and the like, to an ink tank (not shown) arranged on the exterior of the inkjet head 16.
The piezoelectric element 56 has a structure in which a piezoelectric body 56C is arranged between an upper electrode 56A and a lower electrode 56B, and produces mechanical distortion when a drive voltage is applied between the upper electrode 56A and the lower electrode 56B. The mechanical distortion of the piezoelectric element 56 causes the pressure chamber 52 to deform, thereby causing ink contained in the pressure chamber 52 to be ejected from the nozzle 50. When the distorted piezoelectric element 56 is restored to the original state, the interior of the pressure chamber 52 is refilled with ink from the common flow channel 58 through the supply port 54. If the diaphragm 55 is made of a metal material, the diaphragm 55 can also serve as the lower electrode 56B.
The inkjet head 16 shown in
As shown in
The gas chamber 60 arranged for each head module 16A can be supplied and filled with dry gas through the dry gas supply port 62 shown in
The gas chamber 60 can have a structure configured to collectively cover all of the piezoelectric elements 56 arranged in the head module 16A, or can have a structure including a plurality of compartments. Furthermore, it is also possible to adopt a mode in which one integrated gas chamber 60 is arranged for a plurality of head modules 16A.
In the structure in which the gas chamber 60 is divided into compartments, it is possible that the gas chamber 60 is divided in accordance with the arrangement of the piezoelectric elements 56. It is also possible to adopt a mode in which one compartment of the gas chamber 60 is used for one row of the piezoelectric elements 56 arranged in an oblique direction (see
It is possible to form the gas chamber 60 in a layering process when forming the inkjet head 16, or alternatively, it is also possible that a separately formed gas chamber 60 is bonded to the inkjet head 16.
Next, a dry gas supply unit configured to supply dry gas to the gas chamber 60 of the inkjet head 16 is described in detail.
The dry gas supply unit 70 shown in
In the present embodiment, the “dry gas” is defined as a gas of which the dew point is not higher than −4.4° C., and displays a function of reducing the humidity in the atmosphere by absorbing moisture in the atmosphere. The dew point of the dry gas can be determined by direct measurement using a dew point thermometer, or by calculation to obtain the water vapor pressure from the gas temperature and the relative humidity of the gas and then determine the temperature at which the obtained water vapor pressure is equal to the saturation pressure of water vapor.
More specifically, the dry gas supply unit 70 includes: a compressor 72 configured to generate compressed air; a filter 74 configured to remove foreign material, such as dirt, from the compressed air generated by the compressor 72; and an air drier 76 configured to generate dry air from the compressed air from which the foreign material has been removed by the filter 74.
The air drier 76 is connected to the gas chamber 60 at the dry gas supply port 62 through a dry gas supply flow channel 78. The dry gas supply flow channel 78 is provided with a supply flow valve 80, which can be switched between connection and disconnection of the air drier 76 and the gas chamber 60.
When the dry gas is supplied to the gas chamber 60, the supply flow valve 80 is opened and the dry gas is introduced into the gas chamber 60 from the air drier 76. On the other hand, when the supply of dry gas to the gas chamber 60 is halted, the supply flow valve 80 is closed. While the supply of dry gas to the gas chamber 60 is halted, the closure of the supply flow valve 80 prevents moisture from penetrating into the gas chamber 60 that is in the low humidity state.
The gas return port 64 of the gas chamber 60 is connected to one end of the return flow channel 82, and the other end of the return flow channel 82 is open to the external air at the gas outlet 40. The return flow channel 82 is provided with a return flow valve 84, which can be switched between connection and disconnection of the gas chamber 60 and the external air.
The gas outlet 40, which is the end of the return flow channel 82 that is open to the external air, is arranged to the outside of the print unit 17 as shown in
In the inkjet recording apparatus in the related art (e.g., in Japanese Patent Application Publication No. 2004-322605), there are concerns about condensation on the nozzle surface due to air having high humidity expelled from the casing. Furthermore, there are also concerns about the effects of the flow of air on the periphery of the nozzles. According to the present embodiment, these problems can be resolved by arranging the gas outlet 40, which is the end of the return flow channel 82 open to the external air, to the exterior of the print unit 17.
When the dry gas is supplied to the gas chamber 60, the return flow valve 84 is opened, thereby preventing the interior of the gas chamber 60 from assuming a high pressure. When the supply of dry gas to the gas chamber 60 is halted, the return flow valve 84 is closed. While the supply of dry gas to the gas chamber 60 is halted, the closure of the return flow valve 84 prevents reverse flow of moisture from the external air into the gas chamber 60 that is in the low humidity state.
The return flow channel 82 is provided with a humidity sensor 86 configured to measure the humidity of the gas returned from the gas chamber 60 to obtain humidity information. The humidity in the gas chamber 60 is ascertained on the basis of the humidity information obtained through the humidity sensor 86.
The dry gas supply flow channel 78 is provided with a relief valve 88 arranged between the air drier 76 and the supply flow valve 80. If the pressure inside the gas chamber 60 is greater than a threshold pressure, for instance, due to blockage of the gas return port 64 on the gas chamber 60, then the relief valve 88 opens and the dry gas supply flow channel 78 is opened to the external air, and breakage of the gas chamber 60, and the like, is prevented.
In the inkjet recording apparatus in the related art (e.g., in Japanese Patent m Application Publication No. 2004-322605), if the discharge port of the casing is blocked, the interior of the casing assumes a high pressure and hence there is a risk of mechanical breakage of the inkjet head. According to the present embodiment, this problem can be resolved by arranging the relief valve 88 on the dry gas supply flow channel 78 between the air drier 76 and the supply flow valve 80.
The compressor 72 introduces compressed air of about 0.5 MPa into the air drier 76. The compressor 72 has a drain for water condensed when the air is compressed.
The filter 74 can employ a composition including an air filter, which removes dust from the air, and an oil filter, which removes an oil component from the air. It is also possible to adopt a mode in which the filter 74 is incorporated into the air drier 76. The filter 74 has a drain for water and captured dust and oil component.
The air drier 76 employs a cooling air drier which removes the water content in the air by lowering the temperature of the air. It is also possible that the air drier 76 employs a moisture absorption type of air drier. The dry gas generated by the air drier 76 is introduced into the gas chamber 60 through the dry gas supply flow channel 78 and the dry gas supply port 62.
It is desirable that the dry gas supply flow channel 78 has been degreased. It is further desirable that the flow channel pipes and members on the upstream side of the gas chamber 60 in terms of the flow direction of the gas have been degreased.
The supply flow valve 80 arranged in the dry gas supply flow channel 78 and the return flow valve 84 arranged in the return flow channel 82 can employ control valves which are controllable to open and close by control signals (for example, electromagnetic valves). It is also possible that at least one of the supply flow valve 80 and the return flow valve 84 employs a manual valve, which is manually opened and closed.
Each of the supply flow valve 80 and the return flow valve 84 can employ any of a normally closed type, normally open type and latch type of valve. It is desirable that the supply flow valve 80 and the return flow valve 84 employ the normally closed type of valves, which are closed while electric power is not supplied. It is thereby possible that, while the electric power is off, the dry gas supply flow channel 78 and the gas chamber 60 are disconnected, the return flow channel 82 and the gas chamber 60 are also disconnected, and therefore outflow of dry gas from the gas chamber 60 and inflow of gas having high humidity into the gas chamber 60 are prevented. It is also desirable that the supply flow valve 80 and the return flow valve 84 employ the latch type of valves, which have little effects of heat generation when opened.
The humidity sensor 86 is arranged in order to monitor whether or not the dry gas is being supplied to the gas chamber 60. The humidity sensor 86 is arranged at a downstream side of the air drier 76 in terms of the flow direction of the gas, and more desirably, at a downstream side of the gas chamber 60.
A moisture absorbing member 90 is arranged in the gas chamber 60. While the dry gas is not being supplied to the gas chamber 60, even if moisture penetrates into the gas chamber 60 through gaps, the moisture absorbing member 90 absorbs this moisture and keeps the humidity inside the gas chamber 60 uniform. The moisture absorbing member 90 is installed on a wall which constitutes the gas chamber 60. The moisture absorbing member 90 can be restored to have prescribed moisture absorbing properties by passing the dry gas in the gas chamber 60.
Although
In other words, it is preferable that the moisture absorbing member 90 is arranged in the path of dry gas (including the gas chamber 60), from the supply flow valve 80 to the return flow valve 84.
Although the dried air (which has undergone the moisture removal process) is employed as the dry gas supplied to the gas chamber 60 in the present embodiment, it is also possible to employ an inert gas, such as nitrogen or argon, or the like as the dry gas. The dry gas employed in the present embodiment has the dew point of not higher than −15° C., and the dew point of the gas in the gas chamber 60 is not higher than −4.4° C.
The reference value of the “dew point of dry gas” described above can be determined from the ambient conditions when the operating life of the piezoelectric elements 56 (see
As shown in Table 1, under the conditions where the relative humidity is 40% at the ambient temperature of 30° C. (i.e., the dew point of dry gas is 14.9° C.), the operating life of the piezoelectric elements is estimated to be about 7.5 years.
According to these test results, if the dew point of the dry air for removing moisture from the periphery of the piezoelectric elements 56 is not higher than 15° C. (14.9° C.), then it is possible to obtain the operating life of the piezoelectric elements that is sufficient in practical terms.
Moreover, using a module incorporating the moisture absorbing member 90 (the structure corresponding to the inkjet head 16 shown in
As shown in Table 2, if the relative humidity of dry gas is not higher than 10% (the dew point is not higher than −4.4° C.) at first, it is possible to maintain the relative humidity of the air inside the module at not higher than 40% for three months after the supply of dry gas is halted, and it is possible to obtain an allowable period of halting supply of dry gas that is sufficient in practical terms. It is considered that the lower the relative humidity of dry gas supplied to the module, the drier the state of the moisture absorbing member arranged in the module. More specifically, if the dew point of dry gas supplied to the gas chamber 60 is not higher than −4.4° C., then it is possible to obtain the allowable period of halting supply of dry gas that is sufficient in practical terms.
The communication interface 100 is an interface unit for receiving raster image data transmitted from a host computer 114. The communication interface 100 can employ a serial interface, such as a USB (Universal Serial Bus), or a parallel interface, such as a Centronics device. It is also possible to install a buffer memory (not shown) for achieving high-speed communications in the communication interface 100.
The system controller 102 is constituted of a central processing unit (CPU) and peripheral circuits of same, and the like, and functions as a control device which controls the whole of the inkjet recording apparatus 10 in accordance with a prescribed program, as well as functioning as a calculating device which performs various calculations and also functioning as a memory controller for the image memory 110 and the ROM 112.
More specifically, the system controller 102 controls the various sections, such as the communication interface 100, the conveyance control unit 104, and the like, as well as controlling communications with the host computer 114 and read and writing to and from the image memory 110 and the ROM 112, and the like, and generating control signals which control the respective units described above.
The image data sent from the host computer 114 is inputted to the inkjet recording apparatus 10 through the communication interface 100, and prescribed image processing is carried out by the image processing unit 106.
The image processing unit 106 is a control unit which has signal (image) processing functions for carrying out various treatments, corrections and other processing in order to generate a signal for controlling printing from the image data, and which supplies the generated print data (dot data) to the head drive unit 108.
When prescribed signal processing has been carried out in the image processing unit 106, the volume of droplet to be ejected (droplet ejection volume) and the ejection timing of the inkjet head 16 are controlled through the head drive unit 108 on the basis of the print data (halftone image data).
Thereby, desired dot sizes and dot arrangements are achieved. The head drive unit 108 shown in
The conveyance control unit 104 controls the conveyance timing and conveyance speed of the recording medium 12 (see
The image memory (temporary storage memory) 110 has the functions of a temporary storage device for temporarily storing the image data inputted through the communication interface 100, and the functions of a development area for various programs stored in the ROM 112 and a calculation work area for the CPU (for example, a work area for the image processing unit 106). A volatile memory (RAM) which can be read from and written to sequentially is used as the image memory 110.
The ROM 112 stores the program which is executed by the CPU of the system controller 102, and various data and control parameters, and the like, which are necessary for controlling the respective sections of the inkjet recording apparatus 10, and performs reading and writing of data through the system controller 102. The ROM 112 is not limited to a memory constituted of semiconductor devices, and can also employ a magnetic medium, such as a hard disk. Furthermore, the storage unit can also include an external interface and use a detachable storage medium.
The parameter storage unit 118 stores various control parameters which are necessary for the operation of the inkjet recording apparatus 10. The system controller 102 reads out parameters required for control purposes, as appropriate, and updates (rewrites) parameters as and where necessary.
The program storage unit 120 is a storage device which stores the control programs for operating the inkjet recording apparatus 10. In controlling the respective units of the inkjet recording apparatus 10, the system control unit 102 (or respective units of the inkjet recording apparatus 10 themselves) reads out the required control program from the program storage unit 120 and the control program is duly executed.
The display 122 is a device which displays various information sent from the system controller 102, and employs a generic display device, such as an LCD monitor. The display mode of the display unit 122 can employ lighting of lamps (flashing, switching off). Moreover, it is also possible that the display unit 122 is provided with a sound (voice) output device, such as a speaker.
An input interface 124 employs an information input device, such as a keyboard, mouse, joystick, or the like. The information inputted through the input interface 124 is sent to the system controller 102.
A valve control unit 126 sends control signals to the supply flow valve 80 and the return flow valve 84 shown in
A dry gas generation control unit 128 controls operation of the compressor 72 and the air drier 76 shown in
More specifically, when the dry gas is generated to be sent into the gas chamber 60, the compressor 72 is operated, compressed air is introduced into the air drier 76, the air drier 76 is operated, and the dry gas is generated. In other words, the compressor 72 and the air drier 76 function as the dry gas generation unit.
The humidity sensor 86 measures the humidity of the gas returned from the gas chamber 60 and sends the measurement results (humidity information) to the system controller 102. The system controller 102 judges whether or not there is an abnormality in the humidity inside the gas chamber 60 on the basis of the humidity information obtained from the humidity sensor 86. If there is an abnormality in the humidity in the gas chamber 60, an error message is displayed on the display unit 122.
Next, the ventilation function employed in the inkjet recording apparatus 10 (inkjet head 16) according to the present invention is described in detail. The ventilation function described below keeps the atmosphere around the piezoelectric elements 56 arranged in the inkjet head 16 to a low-humidity state in order to avoid performance deterioration or breakage of the piezoelectric elements 56 due to application of the drive voltage, which can readily occur in a state of high humidity.
The low-humidity state is a state where the humidity is at least lower than the peripheral humidity of the print unit 17 (17′), and desirably a state where the dew point is not higher than −4.4° C.
When the ventilation function is halted, the supply flow valve 80 of the dry gas supply flow channel 78 and the return flow valve 84 of the return flow channel 82 are closed so as to prevent moisture from penetrating into the gas chamber 60 while the supply of dry gas to the gas chamber 60 is halted.
Thus, by preventing penetration of moisture into the gas chamber 60 while the supply of dry gas is halted, then even if the inkjet head 16 (piezoelectric elements 56) is operated while the ventilation function is halted or immediately after starting implementation of the ventilation function, the piezoelectric elements 56 are prevented from breaking the moment they start operation.
During the operation of the inkjet head 16, the ventilation function is implemented continuously. The operation of the inkjet head 16 includes an initialization operation when starting up the inkjet recording apparatus 10 and a maintenance operation during a pause in image formation, as well as ink ejection for the purpose of image formation. More specifically, the operation of the inkjet head 16 includes cases where a voltage of any kind is applied between the upper electrode 56A and the lower electrode 56B of the piezoelectric element 56, for instance, application of voltage in order to maintain a steady state of the piezoelectric element 56, or application of voltage when causing the meniscus to vibrate without causing ink to be ejected, and so on.
As shown in
Next, the air drier 76 is started (step S14 in
When the prescribed volume of dry gas has been generated, the supply flow valve 80 and the return flow valve 84 are opened (step S18).
Thereupon, the humidity measured by the humidity sensor 86 in
In the ventilation function according to the present embodiment, the humidity measured by the humidity sensor 86 is regarded as the humidity of the gas in the gas chamber 60. It is also possible that the humidity of the gas in the gas chamber 60 is taken as the value obtained by multiplying the humidity measured by the humidity sensor 86 by a prescribed coefficient, or is taken as the value obtained by adding a prescribed coefficient to the humidity measured by the humidity sensor 86.
On the other hand, in step S20, if the humidity measured by the humidity sensor 86 exceeds the threshold humidity (in a high-humidity state where the measured humidity is higher than the threshold humidity) (No verdict), the procedure advances to step S26 in
Possible examples of the error reporting are a mode where an error message is displayed on the display unit 122 shown in
When the error is reported in step S26, the procedure advances to step S28 (ventilation function halt sequence), and the ventilation function is terminated (step S30).
In step S22, if the interior of the gas chamber 60 is judged to have been substituted with the dry gas (Yes verdict), the procedure advances to step S24. On the other hand, if it is judged in step S22 that the interior of the gas chamber 60 has not been substituted with the dry gas (No verdict), then the procedure returns to step S20, and steps S20 and S22 are carried out repeatedly.
It is ascertained whether or not the interior of the gas chamber 60 has been substituted with the dry gas on the basis of the flow volume of the gas flowing in the dry gas supply flow channel 78 in
In step S24, a humidity monitoring sequence is carried out inside the gas chamber 60. More specifically, when the control is shifted to step S24, the interior of the gas chamber 60 is at a prescribed low-humidity state, and it is therefore possible to start the supply of the electric power to the inkjet head 16 to start the operation (application of voltage to the piezoelectric element 56). The details of the humidity monitoring sequence shown in step S24 are described below.
When the prescribed halt conditions are satisfied, the humidity monitoring sequence (step S24) is terminated. When the humidity monitoring sequence has been terminated, the ventilation function halt sequence (step S28) is carried out and the ventilation function is terminated (step S30).
The conditions for halting the ventilation function are, for instance, when the humidity of the gas chamber 60 has exceeded a prescribed humidity, or when the power of the inkjet recording apparatus 10 is turned off, etc.
In step S102 in
When the ventilation halt conditions are satisfied, the procedure transfers to the ventilation function halt sequence (step S200). Firstly, the compressor 72 in
According to the inkjet recording apparatus 10 which is composed as described above, the low humidity state is achieved by supplying the dry gas to the gas chamber 60 in which the piezoelectric elements 56 are accommodated, before operating the inkjet head 16, and the low humidity state of the gas chamber 60 is maintained during the supply of the electric power to the inkjet head 16 (at least during application of voltage to the piezoelectric elements 56). When the supply of dry gas to the gas chamber 60 is halted, the penetration of moisture into the gas chamber 60 that is in the low humidity state is prevented because the supply flow valve 80 and the return flow valve 84 are closed.
Moreover, since a voltage is applied to the piezoelectric elements 56 when a prescribed time has elapsed after starting the supply of dry gas to the gas chamber 60, then even in cases where the gas chamber 60 is in a state of high humidity before the supply of dry gas, the voltage is applied to the piezoelectric elements 56 after the gas chamber 60 has been changed to the low humidity state and breakage or deterioration of performance of the piezoelectric elements 56 is prevented.
Further, by arranging the gas outlet 40 connected to the external air of the return flow channel 82 to the exterior of the print unit 17, condensation on the ink ejection surface due to the gas discharged from the gas outlet 40 is prevented and the effects of the flow of the gas on the ejection of ink are also prevented.
Furthermore, since the relief valve 88 is connected to the dry gas supply flow channel 78, breakage of the gas chamber 60 and the dry gas supply flow channel 78, and the like, is prevented, even in cases where the gas return port 64 or the return flow channel 82 is blocked and the interior of the gas chamber 60 has reached a state of high pressure.
Furthermore, by arranging the moisture absorbing member 90 inside the gas chamber 60, the moisture which has penetrated inside the gas chamber 60 during the halt of the supply of dry gas is removed.
Next, modifications of the dry gas supply unit 70 described above are explained.
The filter type air drier 76′ shown in
In the mode including the filter type air drier 76′, which requires a higher pressure, the regulator 77 having the pressure gauge 79 is necessary on the downstream side of the filter type air drier 76′ in terms of the gas flow direction. Furthermore, in this mode, it is possible to maintain a low humidity state in the gas chamber 60 provided that the dry gas is flowing, and therefore the flow volume sensor 87 is arranged instead of the humidity sensor 86 shown in
In step S20′, if the flow volume measured by the flow volume sensor 87 is less than the threshold flow volume (No verdict), then it is judged that the gas chamber 60 has not reached a prescribed low humidity state, the procedure advances to step S26, and an error is reported. In step S20′, a plurality of judgments are carried out similarly to step S20 shown in
On the other hand, in step S20′, if the flow volume measured by the flow volume sensor 87 is equal to or greater than the threshold flow volume (Yes verdict), then it is judged that the gas chamber 60 has reached the prescribed low humidity state, and the procedure advances to step S22.
On the other hand, if the measured flow volume of the gas is equal to or greater than the threshold flow volume at step S102′ (Yes verdict), then it is judged that the gas chamber 60 is in the prescribed low humidity state and the measurement of the flow volume of the gas returned from the gas chamber 60 is carried out again (step S102′).
According to the first modification of the dry gas supply unit, it is possible to omit the air drier start-up step by arranging the filter type air drier 76′ instead of the cooling type air drier 76. Furthermore, by arranging the flow volume sensor 87 instead of the humidity sensor 86, it is possible to ascertain the humidity inside the gas chamber 60, on the basis of the flow volume of the gas returned from the gas chamber 60.
Next, a second modification of the dry gas supply unit is described.
The dry gas supply unit 70″ shown in
The supply side manifold 92 and the return side manifold 94 can also be replaced with joints.
The composition shown in
According to the second modification of the dry gas supply unit, in the mode which includes the plurality of inkjet heads, or in the mode which includes the inkjet head constituted of the plurality of head modules joined together, the dry gas can be distributed uniformly to the inkjet heads or the head modules, and the gas can be returned from the inkjet heads or the head modules.
In the mode shown in
It is also possible to adopt a mode which includes the cooling air drier 76 (see
Next, a modification of the inkjet recording apparatus is described.
The inkjet heads 16K″, 16C″, 16M″ and 16Y″ are arranged obliquely to the horizontal plane, following the outer circumferential surface of the pressure drum 14″. The inkjet heads 16K″, 16C″, 16M″ and 16Y″ can employ the composition of the inkjet heads 16K, 16C, 16M and 16Y shown in
The recording medium 12 which is paid out from a paper supply unit (not shown) is held on the transfer drum 15A and transferred to the pressure drum 14″. The recording medium 12 on which image formation has been carried out is transferred from the pressure drum 14″ to a transfer drum 15B of a later stage.
It is possible to add processes prior to the image formation (a pre-processing step for the recording medium, and the like) and after the image formation (a drying step, a fixing step, and the like) to the inkjet recording apparatus 10″ shown in
In the embodiments of the present invention, the inkjet recording apparatuses which form color images on recording media and the drive methods for the inkjet heads arranged in the inkjet recording apparatuses have been described by way of example, but the scope of application of the present invention is not limited to the inkjet recording apparatuses.
For example, the present invention can also be applied broadly to any of liquid ejection apparatuses which eject liquid to media by an inkjet method, such as pattern forming apparatuses which form prescribed patterns (mask patterns, wiring patterns, etc.) by means of functional liquids containing resin particles and metal particles.
It should be understood that there is no intention to limit the invention to the specific forms disclosed, but on the contrary, the invention is to cover all modifications, alternate constructions and equivalents falling within the spirit and scope of the invention as expressed in the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2011-249971 | Nov 2011 | JP | national |
