Liquid-jetting apparatus and method of driving the same Number:6,802,589 from the United States Patent and Trademark Office (PTO) owispatent

Title: Liquid-jetting apparatus and method of driving the same

Abstract: The liquid-jetting apparatus has a liquid-jetting head with nozzle openings through which liquid particles are jetted. The liquid-jetting head performs a flushing operation to remove the thickened liquid from the nozzle openings to recover its normal liquid-jetting ability. The flushing operation jets liquid particles having a weight of 10 ng or below successively through the nozzle openings at a jetting speed of 8 m/s or above. The liquid-jetting apparatus is capable of achieving a satisfactory flushing operation to ensure a satisfactory liquid-jetting characteristic by recovering from a thickened state in a liquid in the nozzle openings even if the liquid is un-uniformly thickened in the nozzle openings.

Patent Number: 6,802,589 Issued on 10/12/2004 to Yonekubo,   et al.

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Inventors:	Yonekubo; Shuji (Nagano-Ken, JP); Chang; Junhua (Nagano-Ken, JP); Matsumoto; Keiji (Nagano-Ken, JP)
Assignee:	Seiko Epson Corporation (Tokyo, JP)
Appl. No.:	10/229,262
Filed:	August 28, 2002

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Foreign Application Priority Data

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Aug 29, 2001 [JP]			2001-259638
Dec 28, 2001 [JP]			2001-398899
Jan 15, 2002 [JP]			2002-006066
Feb 21, 2002 [JP]			2002-044851
Jul 05, 2002 [JP]			2002-197447

Current U.S. Class:	347/29 ; 347/10; 347/14; 347/23
Current International Class:	B41J 2/165 (20060101)
Field of Search:	347/35,10,11,14,23,24,27,29,34

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References Cited [Referenced By]

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U.S. Patent Documents

	6036299		March 2000		Kobayashi et al.
	6467865		October 2002		Iwamura et al.

Foreign Patent Documents

	0 788 882		Aug., 1997		EP
	1 000 743		May., 2000		EP
	1 034 934		Sep., 2000		EP

Primary Examiner: Hsieh; Shih-Wen
Attorney, Agent or Firm: Sughrue Mion, PLLC

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Claims

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What is claimed is:

1. A liquid-jetting apparatus comprising: a liquid-jetting head provided with nozzle openings and capable of jetting liquid particles through the nozzle openings; and a recovering unit to recover from a state of thickened liquid in the nozzle openings, the recovering unit including a flushing unit that carries out a flushing operation to jet the liquid in the nozzle openings in minute liquid particles, the minute liquid particle having a weight of less than 10 ng and being jetted at a jetting speed of 8 m/s or above.

2. The liquid-jetting apparatus according to claim 1, wherein the liquid-jetting head has pressure chambers respectively communicating with the nozzle openings and containing the liquid, and pressure generating means to vary pressure in the pressure chambers to jet liquid particles through the nozzle openings; and wherein the flushing unit has a driving unit to drive the pressure generating means for the flushing operation.

3. The liquid-jetting apparatus according to claim 2, wherein the pressure generating means includes piezoelectric members capable of deforming the pressure chambers to jet liquid particles through the nozzle openings, and wherein the driving unit gives a driving signal to the piezoelectric member.

4. The liquid-jetting apparatus according to claim 1, wherein the flushing unit is capable of carrying out the flushing operation selectively in a first flushing mode or a second flushing mode, wherein the flushing operation of the first mode jets a minute liquid particle having a weight of less than 10 ng at a jetting speed of 8 m/s or above, and wherein the flushing operation of the second mode jets a minute liquid particle having a weight of 12 ng or above.

5. The liquid-jetting apparatus according to claim 1, wherein the liquid-jetting head is provided with pressure chambers respectively communicating with the nozzle openings and capable of containing the liquid, and pressure generating means driven by liquid-jetting signals to vary pressure in the pressure chambers such that the liquid particles are jetted through the nozzle openings, wherein the flushing unit drives the pressure generating means by a driving signal for flushing, and wherein the driving signal for flushing is generated independently of the liquid-jetting signal.

6. The liquid-jetting apparatus according to claim 5, wherein a meniscus of the liquid formed in the nozzle opening is retracted greatly immediately before the minute liquid particle is jetted by the flushing unit, and the minute liquid particle is jetted through a central part of the meniscus.

7. A liquid-jetting apparatus comprising: a liquid-jetting head provided with nozzle openings and capable of jetting liquid particles through the nozzle openings; a recovering unit to recover from a state of thickened in a liquid in the nozzle openings, the recovering unit comprising a flushing unit that carries out a flushing operation to jet the liquid in the nozzle openings in minute liquid particles, the minute liquid particle having a weight of 10 ng or below and being jetted at a jetting speed of 8 m/s or above, wherein the liquid-jetting head has pressure chambers respectively communicating with the nozzle openings and containing the liquid, and pressure generating means to vary pressure in the pressure chambers to jet liquid particles through the nozzle openings, wherein the flushing unit has a driving unit to drive the pressure generating means for the flushing operation, wherein the pressure generating means comprises piezoelectric members capable of deforming the pressure chambers to jet liquid particles through the nozzle openings, wherein the driving unit outputs a driving signal to the piezoelectric member, and wherein the driving signal given by the driving unit to the piezoelectric member comprises: a first voltage-raising part to apply a voltage for expanding the pressure chamber so that the pressure in the pressure chamber is reduced to the piezoelectric member, a first voltage holding part to apply a voltage for maintaining the pressure chamber at a reduced pressure to the piezoelectric member, a first voltage-reducing part to apply a voltage for contracting the pressure chamber to raise the pressure in the pressure chamber to a slightly reduced pressure to the piezoelectric member, a second voltage holding part to apply a voltage for maintaining the pressure chamber at the slightly reduced pressure to the piezoelectric member, and a second voltage-reducing part to apply a voltage for setting the pressure chamber in its original state to the piezoelectric member.

8. The liquid-jetting apparatus according to claim 7, wherein the first voltage-raising part of the driving signal has an auxiliary voltage-maintaining part to apply a voltage to the piezoelectric member such that the pressure in the pressure chamber is maintained temporarily at a slightly or moderately reduced pressure during an expansion of the pressure chamber to reduce the pressure in the pressure chamber.

9. A liquid-jetting apparatus comprising: a liquid-jetting head provided with nozzle openings and capable of jetting liquid particles through the nozzle openings; a recovering unit to recover from a state of thickened liquid in the nozzle openings, the recovering unit comprising a flushing unit that carries out a flushing operation to jet the liquid in the nozzle openings in minute liquid particles, the minute liquid particle having a weight of 10 ng or below and being jetted at a jetting speed of 8 m/s or above, the flushing unit is capable of carrying out the flushing operation selectively in a first flushing mode or a second flushing mode; a head moving mechanism to move the liquid-jetting head in a scanning direction; a capping mechanism disposed in a head-moving range in which the liquid-jetting head is able to move and capable of covering the nozzle openings; a timer for measuring a time elapsed after the nozzle openings have been covered with the capping mechanism; and a mode control unit to selectively determine the mode of the flushing operation based on the time measured by the timer, wherein the flushing operation of the first mode jets a minute liquid particle having a weight of 10 ng or below at a jetting speed of 8 m/s or above, and wherein the flushing operation of the second mode jets a minute liquid particle having a weight of 12 ng or above.

10. The liquid-jetting apparatus according to claim 9, wherein the flushing unit carries out the flushing operation in the first flushing mode only when the time measured by the timer is in a range of a predetermined first time and a predetermined second time, and carries out the flushing operation in the second flushing mode when the time measured by the timer is outside the range of the first time and the second time.

11. The liquid-jetting apparatus according to claim 10, wherein the first time is two minutes, and the second time is five minutes.

12. The liquid-jetting apparatus according to claim 9, wherein the flushing unit operates in the first flushing mode in an initial stage of the flushing operation, and starts operating in the second flushing mode a predetermined time after a start of the flushing operation.

13. The liquid-jetting apparatus according to claim 9, wherein the liquid-jetting head has pressure chambers respectively communicating with the nozzle openings and containing the liquid, and pressure generating means to vary pressure in the pressure chambers to jet the liquid particles through the nozzle openings; the flushing unit has a driving unit to drive the pressure generating means; the pressure generating means comprises piezoelectric members capable of deforming the pressure chambers to jet the liquid particles through the nozzle openings; the driving unit outputs a first driving signal to the piezoelectric member for the flushing operation in the first flushing mode, and outputs a second driving signal to the piezoelectric member for the flushing operation in the second flushing mode; and the first driving signal and the second driving signal are made by selectively using parts of a common driving signal.

14. The liquid-jetting apparatus according to claim 13, wherein the first driving signal comprises: a first voltage-raising part to apply a voltage to the piezoelectric member such that the pressure chamber is expanded and the pressure in the pressure chamber is reduced to a reduced pressure, a first voltage holding part to apply a voltage to the piezoelectric member such that the pressure chamber is maintained at the reduced pressure, a first voltage-reducing part to apply a voltage to the piezoelectric member such that the pressure chamber is contracted and the pressure in the pressure chamber is raised to a slightly reduced pressure, a second voltage holding part to apply a voltage to the piezoelectric member such that the pressure chamber is maintained at the slightly reduced pressure, and a second voltage-reducing part to apply a voltage to the piezoelectric member such that the pressure chamber is restored to its original state; and the second driving signal comprises: a first voltage-raising part to apply a voltage to the piezoelectric vibrator such that the pressure chamber is expanded and the pressure in the pressure chamber is reduced to a low pressure, a first voltage holding part to apply a voltage to the piezoelectric vibrator such that the pressure chamber is maintained at the low pressure, a first voltage-reducing part to apply a voltage to the piezoelectric vibrator such that the pressure chamber is contracted and the pressure in the pressure chamber is raised to a high pressure, a second voltage-holding part to apply a voltage to the piezoelectric vibrator such that the pressure chamber is maintained at the high pressure, and a second voltage-raising part to apply a voltage to the piezoelectric vibrator such that the pressure chamber is restored to its original state.

15. A liquid-jetting apparatus comprising: a liquid-jetting head provided with nozzle openings and capable of jetting liquid particles through the nozzle openings; and a recovering unit to recover from a thickened state in a liquid in the nozzle openings, the recovering unit including a flushing unit that carries out a flushing operation to jet the liquid in the nozzle openings in minute liquid particles, wherein a meniscus of the liquid formed in the nozzle opening is retracted greatly immediately before the minute liquid particle is jetted by the flushing unit, and the minute liquid particle is jetted through a central part of the meniscus.

16. A liquid-jetting apparatus comprising: a liquid-jetting head provided with nozzle openings and pressure chambers respectively communicating with the nozzle openings, and capable of varying pressure applied to a liquid contained in the pressure chambers to jet liquid particles through the nozzle openings and of selectively jetting a plurality of kinds of liquid particles respectively having different volumes through each of the nozzle openings; and a flushing control unit capable of controlling a flushing operation such that the liquid-jetting head jets liquid particles through the nozzle openings to recover from a state of thickened liquid in the nozzle openings; wherein the flushing control unit makes the nozzle opening jet at least two kinds of liquid particles among the plurality of kinds of liquid particles respectively having different volumes in one cycle of the flushing operation, wherein the two kinds of liquid particles to be jetted in one cycle of the flushing operation include a liquid particle having a smallest volume among those of the plurality of kinds of liquid particles respectively having different volumes, and wherein the liquid particle having the smallest volume is jetted first in one cycle of the flushing operation.

17. The liquid-jetting apparatus according to claim 16, wherein the liquid particle having the smallest volume is jetted at least twice in one cycle of the flushing operation, and the liquid particles having the smallest volume are jetted first and last, respectively, in one cycle of the flushing operation.

18. A method of driving a liquid-jetting apparatus having a liquid-jetting head provided with nozzle openings and pressure chambers respectively communicating with the nozzle openings, and capable of varying pressure applied to a liquid contained in the pressure chambers to jet liquid particles through the nozzle openings and of selectively jetting a plurality of kinds of liquid particles respectively having different volumes through each of the nozzle openings, and a flushing control unit capable of controlling a flushing operation such that the liquid-jetting head jets liquid particles through the nozzle openings to recover from a state of thickened liquid in the nozzle openings; wherein the flushing operation is executed by the flushing control unit so that at least two kinds of liquid particles among the plurality of kinds of liquid particles respectively having different volumes are jetted in one cycle of the flushing operation, wherein the two kinds of liquid particles to be jetted in one cycle of the flushing operation include a liquid particle having a smallest volume among those of the plurality of kinds of liquid particles respectively having different volumes, wherein the liquid particle having the smallest volume is jetted first in one cycle of the flushing operation.

19. The method of driving a liquid-jetting apparatus according to claim 18, wherein the liquid particle having the smallest volume is jetted at least twice in one cycle of the flushing operation, and the liquid particles having the smallest volume are jetted first and last, respectively, in one cycle of the flushing operation.

20. A liquid-jetting apparatus comprising: a liquid-jetting head provided with nozzle openings and pressure chambers respectively communicating with the nozzle openings, and capable of varying pressure applied to a liquid contained in the pressure chambers to jet liquid particles through the nozzle openings and of selectively jetting a plurality of kinds of liquid particles respectively having different volumes through each of the nozzle openings; and a flushing control unit capable of controlling a flushing operation such that the liquid-jetting head jets liquid particles through the nozzle openings to recover from a thickened state in a liquid in the nozzle openings; wherein the flushing control unit is capable of selecting an optimum flushing mode among a plurality of flushing modes according to a degree of thickening of the liquid in the nozzle opening, and liquid particles among the plurality of kinds of liquid particles respectively having different volumes excluding a liquid particle having a largest volume are jetted for the flushing operation in any one of the plurality of flushing modes.

21. The liquid-jetting apparatus according to claim 20, wherein a volume of the liquid particle to be jetted for the flushing operation is about half a volume of the liquid particle having the largest volume among those of the plurality of kinds of liquid particles respectively having different volumes.

22. The liquid-jetting apparatus according to claim 20, wherein the liquid particle to be jetted for the flushing operation has a smallest volume among those of the plurality of kinds of liquid particles respectively having different volumes.

23. The liquid-jetting apparatus according to claim 20, wherein the liquid particles are jetted for the flushing operation by a jetting operation other than a jetting operation including steps of continuously expanding the pressure chamber to increase a volume of the pressure chamber, holding the pressure chamber in an expanded state, continuously contracting the pressure chamber to reduce the volume of the pressure chamber, holding the pressure chamber in a contracted state, and continuously expanding the pressure chamber.

24. The liquid-jetting apparatus according to claim 23, wherein the jetting operation of jetting the liquid particle for the flushing operation includes steps of continuously expanding the pressure chamber to increase the volume of the pressure chamber, holding the pressure chamber in an expanded state, continuously and moderately contracting the pressure chamber to reduce the volume of the pressure chamber to a middle reduced level, holding the pressure chamber in a moderately contracted state, and continuously and sufficiently contracting the pressure chamber to a greatest reduced level.

25. The liquid-jetting apparatus according to claim 23, wherein the jetting operation of jetting the liquid particle for the flushing operation includes steps of continuously expanding the pressure chamber to increase the volume of the pressure chamber, holding the pressure chamber in an expanded state, continuously and moderately contracting the pressure chamber to a moderately contracted state, holding the pressure chamber in the moderately contracted state, continuously expanding the pressure chamber again to an expanded state, holding the pressure chamber in the expanded state, contracting the pressure chamber again to a contracted state, holding the pressure chamber in the contracted state, and continuously expanding the pressure chamber again.

26. A method of driving a liquid-jetting apparatus having a liquid-jetting head provided with nozzle openings and pressure chambers respectively communicating with the nozzle openings, and capable of varying pressure applied to a liquid contained in the pressure chambers to jet liquid particles through the nozzle openings and of selectively jetting a plurality of kinds of liquid particles respectively having different volumes through each of the nozzle openings, and a flushing control unit capable of controlling a flushing operation such that the liquid-jetting head jets liquid particles through the nozzle openings to recover from a thickened state in a liquid in the nozzle openings, comprising: selecting an optimum flushing mode among a plurality of flushing modes by the flushing control unit according to a degree of thickening of the liquid in the nozzle openings; and executing the flushing operation so that the liquid particles are jetted through the nozzle openings using a selected flushing mode; wherein the liquid particles among the plurality of kinds of liquid particles respectively having different volumes excluding a liquid particle having a largest volume are jetted for the flushing operation in any one of the plurality of flushing modes.

27. The method of driving a liquid-jetting apparatus according to claim 26, wherein a volume of the liquid particle to be jetted for the flushing operation is about half a volume of the liquid particle having the largest volume among those of the plurality of kinds of liquid particles respectively having different volumes.

28. The method of driving a liquid-jetting apparatus according to claim 26, wherein the liquid particle to be jetted for the flushing operation is a liquid particle having a smallest volume among those of the plurality of kinds of liquid particles respectively having different volumes.

29. The method of driving a liquid-jetting apparatus according to claim 26, wherein the liquid particles are jetted for the flushing operation by a jetting operation other than a jetting operation including steps of continuously expanding the pressure chamber to increase a volume of the pressure chamber, holding the pressure chamber in an expanded state, continuously contracting the pressure chamber to reduce the volume of the pressure chamber, holding the pressure chamber in a contracted state, and continuously expanding the pressure chamber.

30. The method of driving a liquid-jetting apparatus according to claim 29, wherein the jetting operation of jetting the liquid particle for the flushing operation includes steps of continuously expanding the pressure chamber to increase the volume of the pressure chamber, holding the pressure chamber in an expanded state, continuously and moderately contracting the pressure chamber to reduce the volume of the pressure chamber to a middle reduced level, holding the pressure chamber in a moderately contracted state, and continuously and sufficiently contracting the pressure chamber to a greatest reduced level.

31. The method of driving a liquid-jetting apparatus according to claim 29, wherein the jetting operation of jetting the liquid particle for the flushing operation includes steps of continuously expanding the pressure chamber to increase the volume of the pressure chamber, holding the pressure chamber in an expanded state, continuously and moderately contracting the pressure chamber to a moderately contracted state, holding the pressure chamber in the moderately contracted state, continuously expanding the pressure chamber again to an expanded state, holding the pressure chamber in the expanded state, contracting the pressure chamber again to a contracted state, holding the pressure chamber in the contracted state, and continuously expanding the pressure chamber again.

32. A liquid-jetting apparatus comprising: a liquid-jetting head provided with nozzle openings and pressure chambers respectively communicating with the nozzle openings, and capable of varying pressure applied to a liquid contained in the pressure chambers by pressure generating means to jet liquid particles through the nozzle openings, and of selectively jetting a plurality of kinds of liquid particles respectively having different volumes through each of the nozzle openings; a driving signal generating unit capable of selectively generating driving signals respectively having different frequencies for driving the pressure generating means; a cleaning control unit capable of carrying out a cleaning operation that draws out the liquid through the nozzle openings by suction; and a flushing control unit capable of carrying out a flushing operation that operates the pressure generating means such that the liquid-jetting head jets liquid particles through the nozzle openings into a non-recording region; wherein, after a cleaning operation has been carried out by the cleaning control unit, the flushing control unit carries out a flushing operation by making the driving signal generating unit generate a driving signal of a frequency other than a highest frequency among those of the driving signals that can be generated by the driving signal generating unit to jet liquid particles having a smallest volume among those of the plurality of kinds of liquid particles respectively having different volumes.

33. The liquid-jetting apparatus according to claim 32, wherein the driving signal for driving the pressure generating means for the flushing operation has a lowest frequency among those of the driving signals that can be generated by the driving signal generating unit.

34. The liquid-jetting apparatus according to claim 32, wherein the driving signal for driving the pressure generating means for the flushing operation is used also for driving the pressure generating means in a high-quality recording mode.

35. The liquid-jetting apparatus according to claim 32, wherein the driving signal for driving the pressure generating means for the flushing operation is used exclusively for the flushing operation.

36. The liquid-jetting apparatus according to claim 32, wherein a frequency of the driving signal for driving the pressure generating means for the flushing operation is in a range of 0.1 to 3 kHz.

37. The liquid-jetting apparatus according to claim 32, wherein the liquid particle used for the flushing operation has a weight in a range of 1 to 20 ng.

38. The liquid-jetting apparatus according to claim 32, wherein each of the nozzle openings jets liquid particles 1000 times or above for the flushing operation.

39. The liquid-jetting apparatus according to claim 32 further comprising a minute-vibration control unit that applies a minute-vibration pulse by using a driving signal generated by the driving signal generating unit to the pressure generating means to vibrate a meniscus of the liquid in the nozzle opening for slight vibrations after completing the flushing operation.

40. The liquid-jetting apparatus according to claim 39, wherein, after the minute-vibration control unit has completed a minute-vibration operation, the flushing control unit makes the driving signal generating unit generate a driving signal of a frequency higher than that of the driving signal used for jetting the liquid particle having the smallest volume for flushing to jet a liquid particle having a volume larger than that of the liquid particle having the smallest volume through the nozzle opening into the non-recording region for a second flushing operation.

41. The liquid-jetting apparatus according to claim 40, wherein the second flushing operation uses a driving signal of the highest frequency among those of driving signals that can be generated by the driving signal generating unit to jet a liquid particle having a largest volume among those of the plurality of kinds of liquid particles respectively having different volumes through the nozzle opening.

42. The liquid-jetting apparatus according to claim 32 further comprising a stationary-state control unit capable of holding the pressure generating means in a stationary state for a predetermined time after completing the flushing operation.

43. The liquid-jetting apparatus according to claim 42, wherein the predetermined time is one second or longer.

44. A method of driving a liquid-jetting apparatus having a liquid-jetting head provided with nozzle openings, pressure chambers respectively communicating with the nozzle openings and pressure generating means capable of varying pressure applied to a liquid contained in the pressure chambers to jet liquid particles through the nozzle openings, and capable of selectively jetting a plurality of kinds of liquid particles respectively having different volumes through each of the nozzle openings, a driving signal generating unit to generate a driving signal for driving the pressure generating means, capable of selectively generating driving signals respectively having different frequencies, comprising: a cleaning step of cleaning the nozzle openings by drawing out the liquid through the nozzle openings by suction; and a flushing step of, after completing the cleaning step, jetting liquid particles having a smallest volume among those of the plurality of kinds of liquid particles respectively having different volumes through the nozzle openings into a non-recording region for a flushing operation by making the driving signal generating unit generate a driving signal of a frequency other than a highest frequency among those of the driving signals that can be generated by the driving signal generating unit.

45. The method of driving a liquid-jetting apparatus according to claim 44, wherein the driving signal to be used for the flushing operation has a lowest frequency among those of the driving signals that can be generated by the driving signal generating unit.

46. The method of driving a liquid-jetting apparatus according to claim 44, wherein the driving signal to be used for the flushing operation is used also for driving the pressure generating means in a high-quality recording mode.

47. The method of driving a liquid-jetting apparatus according to claim 44, wherein the driving signal for driving the pressure generating means for the flushing operation is used exclusively for the flushing operation.

48. The method of driving a liquid-jetting apparatus according to claim 44, wherein the frequency of the driving signal for driving the pressure generating means for the flushing operation is in a range of 0.1 to 3 kHz.

49. The method of driving a liquid-jetting apparatus according to claim 44, wherein the liquid particle used for the flushing operation have a weight in a range of 1 to 20 ng.

50. The method of driving a liquid-jetting apparatus according to claim 44, wherein each of the nozzle openings jets liquid particles 1000 times or above for the flushing operation.

51. The method of driving a liquid-jetting apparatus according to claim 44 further comprising a minute-vibration step of applying a minute-vibration pulse by using a driving signal generated by the driving signal generating unit to the pressure generating means to vibrate a meniscus of the liquid in the nozzle opening for slight vibrations after completing the flushing operation.

52. The method of driving a liquid-jetting apparatus according to claim 51 further comprising a second flushing step of, after the minute-vibration step has been completed, making the driving signal generating unit generate a driving signal of a frequency higher than that of the driving signal used for jetting the liquid particle having the smallest volume for flushing to jet a liquid particle having a volume larger than that of the liquid particle having the smallest volume through the nozzle opening into the non-recording region.

53. The method of driving a liquid-jetting apparatus according to claim 52, wherein the second flushing step uses a driving signal of the highest frequency among those of driving signals that can be generated by the driving signal generating unit to jet a liquid particle having a largest volume among those of the plurality of kinds of liquid particles respectively having different volumes through the nozzle opening.

54. The method of driving a liquid-jetting apparatus according to claim 44 further comprising a stationary-state control step of holding the pressure generating means in a stationary state for a predetermined time after completing the flushing operation.

55. The method of driving a liquid-jetting apparatus according to claim 54, wherein the predetermined time is one second or longer.

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Description

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BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid-jetting apparatus including a liquid-jetting head provided with nozzle openings through which liquid particles are jetted, and a method of driving the liquid-jetting apparatus.

2. Description of the Related Art

An ink-jet recording apparatus, such as an ink-jet printer or plotter, is a representative example of a liquid-jetting apparatus. The ink-jet recording apparatus moves a recording head, i.e., a liquid-jetting head, in a scanning direction, moves a recording sheet (printable recording medium) in a feed direction, jets ink particles through the nozzle openings of the recording head as the recording head is moved in the scanning direction to print images (characters) on a recording sheet. Ink particles (liquid particles) are jetted, for example, by changing the pressure of the ink in pressure chambers communicating with the nozzle openings, respectively.

The pressure of the ink is changed by a pressure-generating element, such as a piezoelectric vibrator (piezoelectric member). The piezoelectric vibrator is transformed when a driving pulse is applied thereto to change the volume of the pressure chamber. Consequently, the pressure of the ink contained in the pressure chamber changes to jet an ink particle through the nozzle opening.

Since the ink in the nozzle openings of the recording head is exposed to the atmosphere, the solvent, such as water, of the ink evaporates gradually and the viscosity of the ink in the nozzle openings increases, which deteriorates the image quality of recorded images. When the viscosity of the ink filling the nozzle opening is excessively high, it is possible that an ink particle jetted through the nozzle opening deviates from a normal direction.

Therefore, measures are taken for the ink-jet recording apparatus to prevent increase in the viscosity of the ink filling the nozzle openings. The measures include a flushing operation for forcibly jetting the ink having an increased viscosity to a non-recording region outside a recording region or a stirring operation for stirring the ink by vibrating meniscus of the ink. The meniscus is the exposed free surface of the ink in the nozzle opening.

The conventional flushing operation uses a jetting waveform included in a driving signal which is also used for jetting an ink particle for a recording operation.

Generally, a driving signal for driving an ink-jet device to jet an ink particle for recording has a first voltage-raising part to apply a voltage to the piezoelectric member such that the pressure chamber is expanded and the pressure in the pressure chamber is reduced to a reduced pressure, a first voltage holding part to apply a voltage to the piezoelectric member such that the pressure chamber is maintained at the reduced pressure, a first voltage-reducing part to apply a voltage to the piezoelectric member such that the pressure chamber is contracted and the pressure in the pressure chamber is raised to a raised pressure, a second voltage holding part to apply a voltage to the piezoelectric member such that the pressure chamber is maintained at the raised pressure, and a second voltage-raising part to apply a voltage to the piezoelectric member such that the pressure chamber is restored to its original state.

Generally, ink particles including those for the flushing operation are jetted at a jetting speed on the order of 7 m/s, and the weight of the ink particles is, for example, 13 ng.

Usually, parts of the recording head corresponding to the nozzle openings are covered with a cap.

The inventors of the present invention acquired knowledge that it is possible that thickenings of lines or failure in forming dots occurs during printing after removing the cap if the ink has a high pigment concentration. The thickening of lines and failure in forming dots occur when bubbles are formed in the nozzle openings. The inventors of the present invention made the following analytical studies to find what forms bubbles in the nozzle opening.

The solvent, such as water, of the ink filling the nozzle opening covered with a cap and forming a meniscus evaporates and the viscosity of the ink increases. An ink particle jetted through the nozzle opening deviates from a normal direction or the nozzle opening is clogged with the ink if the viscosity of the ink is thus increased.

Increase in the viscosity of the ink starts from a peripheral part of the nozzle opening. Whereas the viscosity of the ink in a peripheral part of the meniscus started to increase in about two minutes after the nozzle opening has been covered with the cap, the viscosity of the ink in a central did not start to increase in about five minutes after the nozzle opening has been covered with the cap. Thus, the viscosity of the ink forming the meniscus increases un-uniformly in a period of two to five minutes after the nozzle opening has been covered with the cap.

An ordinary flushing operation applies pressure to the ink so that the entire meniscus is pushed out of the nozzle opening as shown in FIG. 9(b). Therefore, if the viscosity of the ink in a peripheral part of the nozzle opening and that of the ink in a central part of the nozzle opening are differently increased, the meniscus is un-uniformly deformed by the flushing operation and the meniscus is liable to break. If the flushing operation is continued with the meniscus in an easily breakable state, it is highly possible that the ink adheres to the periphery of the outlet of the nozzle opening, the meniscus is broken and, eventually, bubbles are formed in the ink.

Actually, printing troubles, such as the thickening of printed lines and failure in printing dots, occur only in two to five minutes after the nozzle openings have been covered with the cap.

Therefore, when the viscosity of the ink forming the meniscus is expected to be un-uniformly increased, the flushing operation must supply energy sufficient to overcome the strength of a film of the ink having the increased viscosity to the ink filling a central part of the nozzle opening to jet an ink particle, and the flushing operation must be continued to remove gradually the ink having the increased viscosity forming the peripheral part of the meniscus.

The conventional flushing operation uses large ink particles that are jetted during a printing operation for printing large dots and are capable of exerting a large force enough to blow off the ink of the increased viscosity to achieve flushing in a short time. The term "large dot" signifies the largest dot that can be formed by the relevant ink-jet recording apparatus.

It was found that particles of some ink jetted immediately after the completion of the flushing operation are subject to so called "wet deviation" and reduces printing accuracy if large ink particles are jetted for the flushing operation. The term "wet deviation" signifies the deviation of a jetted ink particle from a normal flying direction due to the drawing effect of the ink adhered to the periphery of the outlet of the nozzle opening during the preceding flushing operation on the jetted ink particle.

The occurrence of wet deviation immediately after the flushing operation may be due to the adhesion of a mist of the ink generated during the flushing operation that jets large ink particles to the periphery of the outlet end of the nozzle opening.

An ink having a high pigment concentration and prone to thicken has a tendency to cause wet deviation immediately after the flushing operation.

Recently, inks having a high pigment concentration have been developed. The use of such an ink having a high pigment concentration will make wet deviation immediately after the flushing operation more serious.

For example, experiment showed that wet deviation occurs when the flushing operation is started after an interval of one second or longer from an ink-jetting cycle preceding the flushing operation if the flushing operation that jets large ink particles uses an ink having a high pigment concentration of ten-odd percent; that is wet deviation occurs inevitably unless the flushing operation that jets large ink particles is started within one second after the preceding ink-jetting cycle, when an ink having a pigment concentration of ten-odd percent is used. The execution of the flushing operation within such a short time after the preceding ink-jetting cycle is practically very difficult or impossible.

Another flushing operation may jet a small ink particle for forming a small dot through the nozzle opening to prevent wet deviation.

However, if an ink that thickens at a high rate is jetted in a small ink particle for the flushing operation, it is possible that some part of the thickened ink remains in the nozzle opening. Moreover, the flushing operation that jets a small ink particle needs a long time. Such a small ink particle is light and is easy to change into a mist. For example, it is possible that a small ink particle changes into a mist, and the mist wets the periphery of the outlet end of the nozzle opening to cause wet deviation, when the distance between the surface, in which the outlets of nozzle openings lie, of a recording head and a member on which an ink particle jetted for the flushing operation falls, such as the surface, on which the ink particle falls, of a cap that covers the surface of the recording head in a non-recording region outside a recording region is relatively long.

Generally, conventional ink-jet recording apparatuses have a function to perform a cleaning operation to remove the ink solidified in the nozzle openings and clogging the nozzle openings and to stop faulty ink jetting attributable to bubbles mixed in the ink in a ink supply passage by covering the surface, in which the nozzle openings open, of the recording head with a capping means and removing the ink from the nozzle openings by suction exerted by a vacuum pump (tube pump), when the nozzle openings are clogged or the ink cartridge is changed.

In this cleaning operation, inks of different colors jetted into the capping means mix together to produce a mixed ink, and the mixed ink adheres to the nozzle openings. Therefore, the conventional ink-jet recording apparatuses perform the flushing operation after the cleaning operation to remove the mixed ink adhering to the nozzle openings. In this flushing operation, ink-jetting pulse signals that are used for making the nozzle openings jet the ink for a printing operation are given to pressurizing members to jet ink particles through the nozzle openings into the non-recording region outside the recording region.

As mentioned above, the conventional flushing operation jets a large ink particle, which is used for forming a large dot by the printing operation, to complete the flushing operation in a short time. An ink-jet recording apparatus capable of changing the frequency of a driving signal to be applied to a pressure-generating element uses a high-frequency driving signal for the flushing operation to reduce time necessary for the flushing operation.

If a large ink particle is jetted for the flushing operation by driving the pressure-generating element by a high-frequency driving signal, it is possible that the meniscus of the ink in the nozzle opening is broken, causing faulty printing, such as failure in properly printing dots. Even after the completion of the cleaning operation, minute bubbles remains in the ink in the nozzle opening and minute bubbles adhere to a part of the wall of the nozzle opening. If the flushing operation using large ink particles is performed under the condition that minute bubbles remain on the wall of the nozzle opening, the meniscus is liable to catch the bubbles because the meniscus is retracted greatly during the flushing operation when a large ink particle is used for the flushing operation. The residual bubbles caught by the meniscus are liable to break the meniscus. Since the meniscus is slightly deformed after the cleaning operation, the jetting characteristic becomes unstable if the flushing operation uses the high-frequency driving signal, which also can be a cause of breakage of the meniscus.

SUMMARY OF THE INVENTION

The present invention has been made in view of the foregoing circumstances and it is therefore an object of the present invention to provide an ink-jet recording apparatus, more broadly, a liquid-jetting apparatus, capable of satisfactorily carrying out an operation of preventing the ink forming a meniscus from thickening to maintain a satisfactory ink-jetting characteristic even if the ink forming a meniscus is thickened un-uniformly.

Another object of the present invention is to provide a liquid-jetting apparatus capable of preventing the wet deviation of a liquid particle jetted immediately after a flushing operation, of optimizing a flushing operation in respect of effect and necessary time, and a driving method of driving the liquid-jetting apparatus.

Still another object of the present invention is to provide a liquid-jetting apparatus capable of achieving a flushing operation without trouble after a cleaning operation, and a driving method of driving the liquid-jetting apparatus.

According to the present invention, a liquid-jetting apparatus comprises: a liquid-jetting head provided with nozzle openings and capable of jetting liquid particles through the nozzle openings; and a recovering unit to recover from a thickened state in a liquid in the nozzle openings, the recovering unit including a flushing unit that carries out a flushing operation to jet the liquid in the nozzle openings in minute liquid particles, the minute liquid particle having a weight of 10 ng or below and being jetted at a jetting speed of 8 m/s or above.

According to the present invention, a liquid-jetting apparatus comprises: a liquid-jetting head provided with nozzle openings and capable of jetting liquid particles through the nozzle openings; and a recovering unit to recover from a thickened state in a liquid in the nozzle openings, the recovering unit including a flushing unit that carries out a flushing operation to jet the liquid in the nozzle openings in minute liquid particles, wherein a meniscus of the liquid formed in the nozzle opening is retracted greatly immediately before the minute liquid particle is jetted by the flushing unit, and the minute liquid particle is jetted through a central part of the meniscus.

Preferably, the liquid-jetting head has pressure chambers respectively communicating with the nozzle openings and containing the liquid, and pressure generating means to vary pressure in the pressure chambers to jet liquid particles through the nozzle openings, and the flushing unit has a driving unit to drive the pressure generating means for the flushing operation.

Preferably, the pressure generating means includes piezoelectric members capable of deforming the pressure chambers to jet liquid particles through the nozzle openings, and the driving unit gives a driving signal to the piezoelectric member.

Preferably, the driving signal given by the driving unit to the piezoelectric member includes: a first voltage-raising part to apply a voltage for expanding the pressure chamber so that the pressure in the pressure chamber is reduced to the piezoelectric member, a first voltage holding part to apply a voltage for maintaining the pressure chamber at a reduced pressure to the piezoelectric member, a first voltage-reducing part to apply a voltage for contracting the pressure chamber to raise the pressure in the pressure chamber to a slightly reduced pressure to the piezoelectric member, a second voltage holding part to apply a voltage for maintaining the pressure chamber at the slightly reduced pressure to the piezoelectric member, and a second voltage-reducing part to apply a voltage for setting the pressure chamber in its original state to the piezoelectric member.

Preferably, the first voltage-raising part of the driving signal has an auxiliary voltage-maintaining part to apply a voltage to the piezoelectric member such that the pressure in the pressure chamber is maintained temporarily at a slightly or moderately reduced pressure during an expansion of the pressure chamber to reduce the pressure in the pressure chamber.

Preferably, the flushing unit is capable of carrying out the flushing operation selectively in a first flushing mode or a second flushing mode. The flushing operation of the first mode jets a minute liquid particle having a weight of 10 ng or below at a jetting speed of 8 m/s or above. The flushing operation of the second mode jets a minute liquid particle having a weight of 12 ng or above.

The liquid-jetting apparatus further comprises: a head moving mechanism to move the liquid-jetting head in a scanning direction; a capping mechanism disposed in a head-moving range in which the liquid-jetting head is able to move and capable of covering the nozzle openings; a timer for measuring a time elapsed after the nozzle openings have been covered with the capping mechanism; and a mode control unit to selectively determine the mode of the flushing operation based on the time measured by the timer.

Preferably, the flushing unit carries out the flushing operation in the first flushing mode only when the time measured by the timer is in a range of a predetermined first time and a predetermined second time, and carries out the flushing operation in the second flushing mode when the time measured by the timer is outside the range of the first time and the second time.

Preferably, the first time is two minutes, and the second time is five minutes.

Preferably, the flushing unit operates in the first flushing mode in an initial stage of the flushing operation, and starts operating in the second flushing mode a predetermined time after a start of the flushing operation.

Preferably, the liquid-jetting head has pressure chambers respectively communicating with the nozzle openings and containing the liquid, and pressure generating means to vary pressure in the pressure chambers to jet the liquid particles through the nozzle openings. The flushing unit has a driving unit to drive the pressure generating means. The pressure generating means includes piezoelectric members capable of deforming the pressure chambers to jet the liquid particles through the nozzle openings. The driving unit gives a first driving signal to the piezoelectric member for the flushing operation in the first flushing mode, and gives a second driving signal to the piezoelectric member for the flushing operation in the second flushing mode. The first driving signal and the second driving signal are made by selectively using parts of a common driving signal.

Preferably, the first driving signal has: a first voltage-raising part to apply a voltage to the piezoelectric member such that the pressure chamber is expanded and the pressure in the pressure chamber is reduced to a reduced pressure, a first voltage holding part to apply a voltage to the piezoelectric member such that the pressure chamber is maintained at the reduced pressure, a first voltage-reducing part to apply a voltage to the piezoelectric member such that the pressure chamber is contracted and the pressure in the pressure chamber is raised to a slightly reduced pressure, a second voltage holding part to apply a voltage to the piezoelectric member such that the pressure chamber is maintained at the slightly reduced pressure, and a second voltage-reducing part to apply a voltage to the piezoelectric member such that the pressure chamber is restored to its original state; and the second driving signal has: a first voltage-raising part to apply a voltage to the piezoelectric vibrator such that the pressure chamber is expanded and the pressure in the pressure chamber is reduced to a low pressure, a first voltage holding part to apply a voltage to the piezoelectric vibrator such that the pressure chamber is maintained at the low pressure, a first voltage-reducing part to apply a voltage to the piezoelectric vibrator such that the pressure chamber is contracted and the pressure in the pressure chamber is raised to a high pressure, a second voltage-holding part to apply a voltage to the piezoelectric vibrator such that the pressure chamber is maintained at the high pressure, and a second voltage-raising part to apply a voltage to the piezoelectric vibrator such that the pressure chamber is restored to its original state.

According to the present invention, a liquid-jetting apparatus comprises: a liquid-jetting head provided with nozzle openings and capable of jetting liquid particles through the nozzle openings; and a recovering unit to recover from a thickened state in a liquid in the nozzle openings, the recovering unit including a flushing unit that carries out a flushing operation to jet the liquid in the nozzle openings in minute liquid particles, wherein the liquid-jetting head is provided with pressure chambers respectively communicating with the nozzle openings and capable of containing the liquid, and pressure generating means driven by liquid-jetting signals to vary pressure in the pressure chambers such that the liquid particles are jetted through the nozzle openings, wherein the flushing unit drives the pressure generating means by a driving signal for flushing, and wherein the driving signal for flushing is generated independently of the liquid-jetting signal.

Preferably, the pressure generating means includes piezoelectric members capable of deforming the pressure chambers to jet liquid particles through the nozzle openings.

Preferably, the minute liquid particle has a weight of 10 ng or below and is jetted at a jetting speed of 8 m/s or above.

Preferably, a meniscus of the liquid formed in the nozzle opening is retracted greatly immediately before the minute liquid particle is jetted by the flushing unit, and the minute liquid particle is jetted through a central part of the meniscus.

According to the present invention, a liquid-jetting apparatus comprises: a liquid-jetting head provided with nozzle openings and pressure chambers respectively communicating with the nozzle openings, and capable of varying pressure applied to a liquid contained in the pressure chambers to jet liquid particles through the nozzle openings and of selectively jetting a plurality of kinds of liquid particles respectively having different volumes through each of the nozzle openings; and a flushing control unit capable of controlling a flushing operation such that the liquid-jetting head jets liquid particles through the nozzle openings to recover from a thickened state in a liquid in the nozzle openings; wherein the flushing control unit makes the nozzle opening jet at least two kinds of liquid particles among the plurality of kinds of liquid particles respectively having different volumes in one cycle of the flushing operation.

Preferably, the two kinds of liquid particles to be jetted in one cycle of the flushing operation include a liquid particle having a smallest volume among those of the plurality of kinds of liquid particles respectively having different volumes.

Preferably, the liquid particle having the smallest volume is jetted first in one cycle of the flushing operation.

Preferably, the liquid particle having the smallest volume is jetted last in one cycle of the flushing operation.

Preferably, the liquid particle having the smallest volume is jetted at least twice in one cycle of the flushing operation, and the liquid particles having the smallest volume are jetted first and last, respectively, in one cycle of the flushing operation.

Preferably, the two kinds of liquid particles to be jetted in one cycle of the flushing operation include a liquid particle having a largest volume among those of the plurality of kinds of liquid particles.

According to the present invention, a method of driving a liquid-jetting apparatus having a liquid-jetting head provided with nozzle openings and pressure chambers respectively communicating with the nozzle openings, and capable of varying pressure applied to a liquid contained in the pressure chambers to jet liquid particles through the nozzle openings and of selectively jetting a plurality of kinds of liquid particles respectively having different volumes through each of the nozzle openings, and a flushing control unit capable of controlling a flushing operation such that the liquid-jetting head jets liquid particles through the nozzle openings to recover from a thickened state in a liquid in the nozzle openings; wherein the flushing operation is executed by the flushing control unit so that at least two kinds of liquid particles among the plurality of kinds of liquid particles respectively having different volumes are jetted in one cycle of the flushing operation.

Preferably, the two kinds of liquid particles to be jetted in one cycle of the flushing operation include a liquid particle having a smallest volume among those of the plurality of kinds of liquid particles respectively having different volumes.

Preferably, the liquid particle having the smallest volume is jetted first in one cycle of the flushing operation.

Preferably, the liquid particle having the smallest volume is jetted last in one cycle of the flushing operation.

Preferably, the liquid particle having the smallest volume is jetted at least twice in one cycle of the flushing operation, and the liquid particles having the smallest volume are jetted first and last, respectively, in one cycle of the flushing operation.

Preferably, the two kinds of liquid particles to be jetted in one cycle of the flushing operation include a liquid particle having a largest volume among those of the plurality of kinds of liquid particles.

According to the present invention, a liquid-jetting apparatus comprises: a liquid-jetting head provided with nozzle openings and pressure chambers respectively communicating with the nozzle openings, and capable of varying pressure applied to a liquid contained in the pressure chambers to jet liquid particles through the nozzle openings and of selectively jetting a plurality of kinds of liquid particles respectively having different volumes through each of the nozzle openings; and a flushing control unit capable of controlling a flushing operation such that the liquid-jetting head jets liquid particles through the nozzle openings to recover from a thickened state in a liquid in the nozzle openings; wherein the flushing control unit is capable of selecting an optimum flushing mode among a plurality of flushing modes according to a degree of thickening of the liquid in the nozzle opening, and liquid particles among the plurality of kinds of liquid particles respectively having different volumes excluding a liquid particle having a largest volume are jetted for the flushing operation in any one of the plurality of flushing modes.

Preferably, a volume of the liquid particle to be jetted for the flushing operation is about half a volume of the liquid particle having the largest volume among those of the plurality of kinds of liquid particles respectively having different volumes.

Preferably, the liquid particle to be jetted for the flushing operation has a smallest volume among those of the plurality of kinds of liquid particles respectively having different volumes.

Preferably, the liquid particles are jetted for the flushing operation by a jetting operation other than a jetting operation including steps of continuously expanding the pressure chamber to increase a volume of the pressure chamber, holding the pressure chamber in an expanded state, continuously contracting the pressure chamber to reduce the volume of the pressure chamber, holding the pressure chamber in a contracted state, and continuously expanding the pressure chamber.

Preferably, the jetting operation of jetting the liquid particle for the flushing operation includes steps of continuously expanding the pressure chamber to increase the volume of the pressure chamber, holding the pressure chamber in an expanded state, continuously and moderately contracting the pressure chamber to reduce the volume of the pressure chamber to a middle reduced level, holding the pressure chamber in a moderately contracted state, and continuously and sufficiently contracting the pressure chamber to a greatest reduced level.

Preferably, the jetting operation of jetting the liquid particle for the flushing operation includes steps of continuously expanding the pressure chamber to increase the volume of the pressure chamber, holding the pressure chamber in an expanded state, continuously and moderately contracting the pressure chamber to a moderately contracted state, holding the pressure chamber in the moderately contracted state, continuously expanding the pressure chamber again to an expanded state, holding the pressure chamber in the expanded state, contracting the pressure chamber again to a contracted state, holding the pressure chamber