Ink jet head, drive method of ink jet head, and ink jet recording apparatus

Information

  • Patent Grant
  • 6309056
  • Patent Number
    6,309,056
  • Date Filed
    Thursday, April 22, 1999
    25 years ago
  • Date Issued
    Tuesday, October 30, 2001
    23 years ago
Abstract
An ink jet head for a printer wherein an ink drop is ejected from a nozzle to fly and land on the recording paper to form an image. The ink jet head includes the nozzle for ejecting ink, an ink channel that communicates with the nozzle, a pair of oscillating plates that are opposing to each other on walls of the ink channel, a pair of electrodes disposed in contact with the oscillating plates, an ink chamber for holding the ink, and an inlet for supplying the ink from the ink chamber to the ink channel. A gap between the electrodes is filled with the ink having a relative dielectric constant higher than air. A voltage is applied between the electrodes.
Description




This application is based on Japanese Patent Application Nos. 10-119435 and 10-119436 filed on Apr. 28, 1998, the contents of which are hereby incorporated by reference.




BACKGROUND OF THE INVENTION




1. Field of the Invention




The present invention relates to ink jet head, drive method thereof, and ink jet recording apparatus for causing ink to fly across a space with the help of deformation of an oscillating plate by means of electrostatic force.




2. Description of the Related Art




An ink jet type recording apparatus causes an ink drop to be ejected from a nozzle and thrown across a space to land on a recording medium to form an image. A number of ink jet heads have been invented to be used on such a recording apparatus. As an example, Japanese laid-open Patent Publication, JP-A-05-50601, discloses an ink jet head that uses an electrostatic actuator that ejects ink with the help of deformation of an oscillating plate by electrostatic force.




This electrostatic ink jet head has a laminar structure composed of three members joined together, i.e., a channel plate provided with a plurality of recesses, a glass substrate positioned opposite to the bottom surface of the recesses, and a cover plate. The recesses form a nozzle that ejects an ink drop, an ink channel that communicates with the nozzle, an oscillating plate that changes the pressure in the ink channel, a common ink chamber where ink is stored, and an inlet that serves as an ink supply port from the common ink chamber to the ink channel. The bottom wall of the ink channel forms an oscillating plate to generate the pressure for ejecting ink. A plurality of ink channels and nozzles are provided in accordance with the number of dots to be printed at a time. Moreover, a first electrode is provided on the surface of the side which is not facing the ink channel, or on the backside of the oscillating plate. A second electrode is provided on the surface of the glass substrate opposing the first electrode separated by a small gap from the first electrode. The recesses provided on the backside of the oscillating plate and the top surface of the substrate also serves as the members to form these electrodes.




The electrostatic type ink jet ejects ink based on the following operating principle to form an image on the recording medium.




First of all, when a voltage is applied between the first electrode and the second electrode by means of a drive circuit, an electrostatic force is generated between the electrodes. Accordingly, the oscillating plate deforms by being drawn in the direction toward the second electrode, or in the direction of moving itself away from the ink channel, which is communicating with the nozzle. At this time, the volume of the ink channel increases. Therefore, ink is drawn through the inlet into the ink channel to fill it up. Next, the application of the voltage between the first and second electrodes as opposing electrodes is terminated and the charges are discharged. The oscillating plate returns to its original position by the restoring force due to its own rigidity. In the mean time, the oscillating plate sharply compresses the volume of the ink channel to generate a pressure. Consequently, the ink stored in the ink channel is ejected, flies across a space, and lands on the recording medium to form an image.




Such an electrostatic jet head has an advantage of allowing us to realize a higher density constitution and to print using a relatively low voltage in comparison with the method of ejecting ink using the deformation of a piezoelectric device.




However, it is necessary to make the gap between the first and second electrodes extremely small in order to reduce the applied voltage on an electrostatic ink jet head. For example, the electrode gap is set to about 0.3 μm. Consequently, it is necessary to produce and assemble individual components such as the channel plate with extreme accuracy in manufacturing the head.




Moreover, since the electrode gap is only about 0.3 μm, there is a danger of causing a short circuit between the first electrode as an individual electrode and the second electrode as a common electrode when the oscillating plate is oscillated. In order to prevent the short circuit, a protective layer can be provided on top of the electrode. However, a problem with the protective layer is that it is susceptible to chronological changes.




The pressure P generated by the electrostatic ink jet head can be expressed by the following formula:








P=


1/2·{∈


r


·∈


o


·(


V/G


)


2


}






wherein the symbol ∈


r


denotes the relative dielectric constant between the opposing electrodes, the symbol ∈


o


denotes the dielectric constant in vacuum, 8.8×10


−12


[F/m], the symbol V denotes the applied voltage [V], and the symbol G denotes the distance between the electrodes [m].




In case of the conventional electrostatic type ink jet head, air is inserted, whose relative dielectric constant is 1, in the gap between the opposing electrodes. Therefore, it is necessary to set the gap G between the electrodes as small as 0.3 μm as mentioned above in order to generate a sufficient pressure to cause ink to fly using, for example, a drive voltage of 40V. The manufacture of such a head has a problem that it requires high precision machining and assembly practices.




Incidentally, the electrostatic type ink jet head uses a constitution of causing the ink in the ink channel to be ejected and fly by means of deforming the oscillating plate as mentioned above. Therefore, a situation can occur, in which the mechanical constitution can no longer follow the demand when the drive frequency of the ink head, or the frequency of the voltage applied between a pair of electrodes is increased in case of continuous printing. Thus, the ink jet head drive frequency is limited by the natural frequency of the ink in the ink channel and the natural frequency of the oscillating plate.




Therefore, a problem has been noted that there is a limit to the improvement of the head response by means of increasing the drive frequency of the ink jet head.




SUMMARY OF THE INVENTION




An object of the invention is to provide an improved apparatus that is capable of solving the problems described above.




Another object of the invention is to provide an ink jet head that allows the use of a larger gap between the electrodes and to make manufacturing easier thus enhancing its reliability.




Another object of the invention is to increase the restoring force of the oscillating plate so that the drive frequency of the ink jet can be improved.




One aspect of the invention is an ink jet head having an ink channel, a pair of oscillating plates, and a pair of electrodes. The ink channel is filled with ink that communicates with a nozzle that ejects ink. The oscillating plates are disposed opposing to each other on walls of the ink channel. The electrodes are provided in contact with the oscillating plates respectively. In addition, a voltage is applied between the electrodes.




Another aspect of the invention is an ink jet recording apparatus having an ink channel, a pair of oscillating plates, a pair of electrodes, and a controller. The ink channel is filled with ink that communicates with a nozzle that ejects ink. The oscillating plates are disposed opposing to each other on walls of the ink channel. The electrodes are disposed in contact with the oscillating plates, respectively. And, the controller controls a voltage to be applied between the electrodes.




Another aspect of the invention is an ink jet head having an ink channel, an oscillating plate, a first electrode, a second electrode, and a third electrode. The ink channel communicates with a nozzle that ejects ink. The oscillating plate is disposed facing the ink channel. The first electrode is disposed on the oscillating plate and a side where the first electrode is disposed is opposite to a side that faces the ink channel. The second electrode is disposed opposing the first electrode. And, the third electrode is located relative to the first electrode on a side opposite to a side the second electrode is located.




Another aspect of the invention is an ink jet recording apparatus having an ink channel, an oscillating plate, a first electrode, a second electrode, a third electrode, and a controller. The ink channel communicates with a nozzle that ejects ink. The oscillating plate is disposed facing the ink channel. The first electrode is disposed on the oscillating plate and a side where the first electrode is disposed is opposite to a side that faces the ink channel. The second electrode is disposed opposing the first electrode. The third electrode is located relative to the first electrode on a side opposite to a side the second electrode is located. And, the controller controls application of voltages on the electrodes.




Another aspect of the invention is a method for driving an ink jet head, including an oscillating plate, that is disposed facing an ink channel, a first electrode disposed on the oscillating plate, a side where the first electrode is disposed being opposite to a side that faces the ink channel, a second electrode that is disposed opposing the first electrode, and a third electrode located relative to the first electrode on a side opposite to a side the second electrode is located. The method contains the steps of a first voltage application step that applies a voltage between the first and second electrodes, and a second voltage application step that applies a voltage between the first and third electrodes.




The objects, characteristics, and advantages of this invention other than those set forth above will become apparent from the following detailed description of the preferred embodiments, which refers to the annexed drawings.











BRIEF DESCRIPTION OF THE DRAWINGS





FIG. 1

is a perspective view of an ink jet printer using an ink jet head according to the embodiment 1;





FIG. 2

is a perspective view of a carriage that contains the ink jet head for one color of the head unit shown in

FIG. 1

;





FIG. 3

is a sectional view of the ink jet head;





FIG. 4

is an exploded perspective view of a channel plate of the ink jet shown in

FIG. 3

;




FIG.


5


A and

FIG. 5B

are sectional views along the line I—I and the line II—II of

FIG. 3

, respectively;





FIGS. 6A

to


6


H are sectional views for describing the manufacturing method of the ink jet head;





FIG. 7

is a block diagram of a drive circuit;





FIG. 8

is a sectional view of an ink jet head according to the embodiment 2;





FIG. 9

is an exploded perspective view of the ink jet head shown in

FIG. 8

;





FIG. 10

is a sectional view of an ink jet head according to the embodiment 3;





FIG. 11

is an exploded perspective view of an ink jet head according to the embodiment 4;





FIG. 12

is a plan view of the ink jet head seen through the channel plate of

FIG. 11

;





FIG. 13

is a sectional view along the line III—III of

FIG. 12

;





FIG. 14

is a sectional view along the line IV—IV of

FIG. 12

;





FIGS. 15A

to


15


C are sectional views for describing the method of manufacturing the channel plate of

FIG. 13

;





FIG. 16

is a block diagram for describing the constitution of the controller of the ink jet printer; and




FIG.


17


A and

FIG. 17B

are expanded sectional views for describing the motions of the oscillating plate when it ejects an ink drop.











DETAILED DESCRIPTION OF THE EMBODIMENTS




The embodiments of this invention will be described below with reference to the accompanying drawings.




Embodiment 1




The ink jet printer


1


shown in

FIG. 1

is intended for forming or recording an image on a sheet


2


, which is a recording medium such as a sheet of paper or an OHP sheet, and consists of a head scanning system and a sheet feeding system.




The head scanning system includes a head unit


3


having an ink jet type print head, a carriage


4


for holding a head unit


3


, a scan shaft


5


and a guide shaft


6


that guide the carriage


4


for reciprocating in parallel with a surface of the sheet


2


where an image is formed, a pulse motor


7


that drives the carriage


4


to reciprocate along the guide shaft


6


, and a timing belt


9


and an idle pulley


8


for converting the rotation of the pulse motor


7


into a reciprocating motion of the carriage


4


. A single print head or a plurality of print heads are provided depending on the number of colors (3, 4 or 7 colors) used.




On the other hand, the sheet feeding system includes a platen


10


that also serves as a guide plate for guiding the sheet


2


along its transportation passage, a pressure plate


11


that holds down the sheet


2


against the platen


10


to prevent the sheet


2


from floating, a discharge roller


12


and a pressure roller


13


for discharging the sheet


2


, a maintenance device


14


for washing the nozzle surface of the head unit


3


that ejects the ink to correct poor ink ejection condition and to restore the nozzle surface to a better condition, and a knob


15


for manually transporting the sheet


2


.




The sheet


2


is transported by means of a manual feeding or a sheet feeding mechanism (not shown) such as a cut sheet feeder into a recording unit where the head unit


3


and the platen


10


are disposed opposing to each other. The transportation of the sheet to the recording unit is controlled by the number of revolutions of a sheet feeding roller driven by a sheet feed motor. The sheet feeding motor and the sheet feeding roller are not shown here.




An electrostatic type ink jet head


31


, which is an electrostatic actuator and will be described later in detailed, is used as the print head of the head unit


3


. Formation or recording of an image is executed by an ink drop ejected from the ink jet head


31


landing on the sheet


2


.




The carriage


4


is driven laterally (main scanning direction) relative to the sheet


2


by means of the pulse motor


7


, the idle pulley


8


, and the timing belt


9


. Accordingly, the head unit


3


mounted on the carriage


4


forms an image of one line in the lateral or main scanning direction on the sheet


2


. In the mean time, the sheet is fed vertically (secondary scanning direction) when recording of one line is completed. Thus, an image can be formed or recorded on the sheet


2


.




The sheet


2


that has passed the recording unit is discharged with the help of the discharge roller


12


provided on the feed direction side, or on the downstream side and the pressure roller


13


that makes contact with the discharge roller


12


under pressure.




As shown in

FIG. 2

, provided in the vicinity of the carriage


4


are an ink cartridge


43


with an air hole


44


, a casing


41


and a casing lid


45


for containing the ink cartridge


43


, an ink supply tube


42


to which the ink cartridge


43


is detachably connected for supplying ink to the ink jet head


31


, a hook


46


and a lid stop


47


used for affixing the casing lid


45


to the casing


41


when the casing lid


45


is closed, and a pressure spring


48


for urging the ink cartridge


43


in the casing


41


while the casing lid


45


is closed, in the direction opposite to the direction of the arrow D


3


, or to the direction of inserting the ink cartridge


43


.




As the carriage


4


having such a constitution moves laterally, or in the direction of the arrow D


1


, one line of image in the main scanning direction is recorded on the sheet


2


. Also, as the sheet


2


is driven in a vertical direction, or the direction of the arrow D


2


, the motion in the secondary scanning direction is executed for recording the next line of image.




Next, the constitution of the ink jet head


31


will be described in detail referring to

FIGS. 3

,


4




5


A and


5


B.




The electrostatic ink jet head


31


shown in

FIG. 3

is of an edge eject type that ejects an ink drop from an nozzle


54


provided on the head side end shown on the left end of the drawing. The ink jet head


31


includes two channel plates


50




a


and


50




b,


each having several recesses, stacked as one on top of the other as shown in FIG.


4


. The channel plates


50




a


and


50




b


are made of single crystal silicone.




By stacking the channel plates


50




a


and


50




b


in such a way that the recesses provided in the inside are facing to each other, they jointly constitute a plurality of nozzles


54


for ink ejection, a plurality of ink channels


51


that respectively communicate with nozzles


54


to generate pressures for ink ejection, a common ink chamber


52


for storing ink supplied from a tank (not shown), and a plurality of inlets


53


, which serve as an ink supply port from the common ink chamber


52


to each ink channel


51


.




For example, the ink channel


51


is formed by matching a recess


51




a


formed in a channel plate


50




a


shown in the upper portion of

FIG. 4 and a

recess


51




b


formed in a channel plate


50




b


shown in the lower portion thereof. The symbol “


58


” shows the ink supply port for introducing ink to the common ink chamber


52


.




A pair of oscillatory plates


55




a


and


55




b


are formed by the upper and lower walls of the ink channel


51


that are opposing to each other. The volume and inner pressure of the ink channel


51


are variable as the oscillating plates


55




a


and


55




b


make minute displacements.




As shown in FIG.


3


and

FIG. 5A

, a first electrode


56


is provided on the inner surface of the oscillating plate


55




a


that faces the ink channel


51


. A second electrode


72


is provided on the inside of the oscillating plate


55




b


as shown in FIG.


3


and FIG.


5


B. Also, the first electrode


56


is a common electrode as shown in

FIG. 3

, and the second electrode


72


is an individual electrode or a drive electrode, both of which are connected to a drive circuit


20


via wires


81


and


82


.




By applying a voltage from the drive circuit


20


to a pair of electrodes


56


and


72


, the pair of oscillating plates


55




a


and


55




b


are attracted to each other so that the volume of the ink channel


51


contracts sharply. The pressure generated at this time causes an ink drop to be discharged from the nozzle


54


. On the other hand, when the application of the voltage to the electrodes is stopped, causing an electric discharge, the oscillating plates


55




a


and


55




b


are restored to their original shapes due to their own restoring forces resulting from their rigidities and increasing the volume of the ink channel


51


. As a result, ink is supplied from the common ink chamber


52


to the ink channel


51


through the inlet


53


.




The first electrode


56


as the common electrode and the second electrode


72


as an individual electrode are exposed to the ink channel


51


to form a portion of the ink passage. In other words, the ink channel


51


is formed between the common electrode and the individual electrode. Therefore, the space between the pair of electrodes


56


and


72


that cause an electrostatic force contains no air but rather is filled with ink.




The relative dielectric constant ∈


r


of water-based ink is about 60 and is larger than the relative dielectric constant ∈


r


of air, which is 1. Obviously, the electrostatic actuator with the constitution stated above has a better efficiency because of the existence of a material with a relative dielectric constant higher than that of air between the electrodes


56


and


72


. As a result, it is possible to use a larger gap G between the electrodes. For example, while the electrode gap of the conventional head is about 0.3 μm, the gap G between the electrodes in case of the head


31


according to the embodiment 1 is almost ten times of that, or about 3 μm.




Next, the method of manufacturing the ink jet head


31


will be described as an example referring to

FIGS. 6A

to


6


H.




The ink jet head


31


is manufactured using various manufacturing processes including the semiconductor device manufacturing process and the micromachine manufacturing process. It goes without saying that the present invention is applicable to an ink jet head manufactured by a method that is not described here.




As shown in

FIG. 6A

, the backside (topside in the drawing) of a substrate


90


made of a single crystal silicon is sandblasted prior to etching. As a result, through-holes


91


for openings used for taking out electrodes as many as the number of the ink channels


51


are formed. At the same time, a through hole


92


for the ink supply port


58


is formed in the same way. The through holes


91


and


92


become slightly tapered narrowing at the distal ends.




As shown in

FIG. 6B

, recesses for constituting the ink channels


51


, the common ink chamber


52


, the inlets


53


, the nozzles


54


and the oscillating plates


55




a,




55




b


are formed by means of anisotropic etching using KOH solution on the channel plates


50




a,




50




b


More specifically, the silicon substrate


90


has a thickness of 200 μm, and its surface orientation is (1, 1, 0). An orifice flat is formed on the (1, 1, 0) surface. A resist


93


is formed on the bottom surface and the top surface (bottom surface in the drawing) of the silicon substrate


90


. Next, the channel pattern is disposed at an angle of 35.3 degrees from the orifice flat. The desired vertical wall structure is formed when etching is done.




Next, the resist


93


is removed as shown in FIG.


6


C. After that, the area indicated by an arrow in the silicon substrate


90


is cut off using a dicer to form the ink eject port (nozzle


54


) as shown in FIG.


6


D.




Next, as shown in

FIG. 6E

, a CrAu layer is formed inside the tapered through hole


91


by means of sputtering or CVD method from the back side of the silicon substrate


90


, while a 0.1 μm CrAu layer for the electrode


56


is formed on the front side of the silicon substrate


90


by means of sputtering or CVD method. Materials such as ITO, SnO


2


, Pt and other low resistance materials in addition to CrAu are applicable to the electrode


56


.




Next, as shown in

FIG. 6F

, a 0.1 μm SiC layer is formed by means of sputtering as a protection layer


94


of the electrode


56


. Although SiO


2


and MgO in addition to SiC can be as the material for forming the protective layer, SiC is most preferable considering its excellent humidity resistance.




Incidentally, the other channel plate


50




b,


which is in a mirror image relation with the channel plate


50




a,


is to be made using the same procedure.




Next, a low melting point glass film


95


is formed on the junction surface between the channel plates


50




a


and


50




b


as shown in FIG.


6


G. When the channel plates


50




a


and


50




b


are joined together as shown in

FIG. 6H

, the ink jet head


31


is completed. The thickness of the oscillating plates


55




a


and


55




b


is 3 μm and the gap G between the electrodes is 3 μm as well.




The ink jet


31


is a high efficient electrostatic actuator due to the constitution, in which the gap between the electrodes


56


and


72


is filled with ink that has a higher relative dielectric constant than air. Therefore, the gap G between the electrodes can be chosen to be extremely larger than that of a conventional head. Accordingly, manufacturing and assembling of the channel plates


50




a


and


50




b


as components of the ink jet head


31


are substantially easier. This also makes the head manufacturing easier and improves the available percentage.




The electrodes


56


and


72


of the ink jet head


31


manufactured as above are connected to the drive circuit


20


as shown in FIG.


7


.




The drive circuit


20


includes a charging circuit


22


connected to a power circuit


21


, a grounded charging circuit


23


, a switching circuit


24


that selectively connects the electrostatic actuator with the electrodes


56


and


72


to the charging circuit


22


or the discharging circuit


23


by means of a switch, a clock circuit


25


for generating clock pulses as the standard for the work timing, and a timer circuit


26


for controlling the charge timing and the discharge timing.




In order to eject ink, it is necessary to cause the pair of oscillating plates


55




a


and


55




b


to be attracted to each other sharply. The drive circuit


20


generates voltage pulses that cause such motions of the oscillating plates


55




a


and


55




b


to control the application and cut-off of the drive voltage to the electrodes


56


and


72


. Therefore, in order to eject ink, first of all, the switch is connected to the charging circuit


22


to apply the voltage on the electrodes


56


and


72


. Then, the voltage is cut-off. After a predetermined time, the switch is connected to the discharging circuit


23


to clear the remaining charge. The switch timing is controlled by the timer circuit


26


.




When a drive voltage of 35V was applied to the ink jet head


31


, it ejected an ink drop of about 60 picolitter. It was necessary to apply a drive voltage of 40V to eject an ink drop of the same volume in case of a conventional ink jet head using a single oscillating plate. Therefore, the ink jet head


31


can use a lower voltage compared to a conventional head. This is because the ink channel


51


of the ink jet head


31


is sandwiched between the pair of oscillating plates


55




a,




55




b


and it is easier to achieve a larger volume change compared to the conventional case where only one oscillating plate is used.




Moreover, while the conventional type ink jet head with 0.3 μm gap G between the electrodes shorted out at 500 million cycles, the ink jet head


31


using 3 μm gap G between the electrodes according to the embodiment 1 still operated without shorting after two billion cycles. It is understood that the chance of the contact between the electrodes


56


and


72


is eliminated and the ink jet head


31


has less chance of being chronologically affected because the ink jet head


31


has a distance between the electrodes much larger than that of the conventional type. Thus, it is possible to provide an ink jet head with a higher reliability in terms of durability.




Embodiment 2




The ink jet head


131


shown in FIG.


8


and

FIG. 9

is of an electrostatic type where an electrostatic actuator is used, and is different from the embodiment 1 in terms of the position of the oscillating plates. Specifically, while the space between the pair of oscillating plates


55




a


and


55




b


forms a portion of the ink passage in the embodiment 1, a pair of oscillating plates


155




a


and


155




b


is disposed slightly apart from the substantial ink passage from an inlet


153


to a nozzle


154


in case of the ink jet head


131


. Therefore, the ink jet head


131


has an improved high speed printing capability compared to the embodiment 1.




As shown in

FIG. 9

, the ink jet head


131


includes two channel plates


150




a


and


150




b


joined together in the vertical direction in the drawing and a nozzle plate


160


, which is joined on the side thereof. The channel plates


150




a


and


150




b


are made of single crystal silicon having a plurality of recesses and the nozzle plate


160


is provided with nozzles


154


.




An extension


161


of the ink channel


151


is extending toward the backside (right side in

FIG. 8

) relative to the nozzle


154


. The top wall and the bottom wall of this extension


161


constitute the oscillating plates


155




a


and


155




b


. Also, the first electrode


156


used as the common electrode is provided on the inside of the oscillating plate


155




a,


while the second electrode


172


used as the individual electrode is provided on the inside of the oscillating plate


155




b.


The inlet


153


is formed on the top surface of the channel plate


150




a


to supply ink from the ink chamber which is not shown.




The nozzle diameter and the inlet diameter are both chosen to be 23 μm. The nozzle plate


160


is made by Ni electro-casting. The methods of etching from the both sides of the silicon substrates, two stage etching, producing the through hole, forming of the electrodes, joining of the substrates, etc. are the same as in the embodiment 1. The materials for the electrodes and protective layer used in the embodiment 1 may be used here as well. The ejection operation is also the same as in the embodiment 1. Specifically, when a specified voltage from the drive circuit


20


is applied between the electrodes


156


and


172


, the pair of oscillating plates


155




a


and


155




b


are attracted to each other so that the volume of the ink channel


151


contracts sharply. The pressure generated at this time causes an ink drop to be discharged from the nozzle


154


. On the other hand, when the application of the voltage between the electrodes


156


and


172


is stopped causing an electric discharge, the oscillating plates


155




a


and


155




b


are restored to their original shapes due to their own restoring forces resulting from their rigidities, and thus increase the volume of the ink channel


151


.




Same as in the embodiment 1, the ink jet head


131


with the aforementioned constitution uses ink with a large relative dielectric constant ∈


r


of about 60 to fill the space between the electrodes


156


and


172


. As a result, the gap G between the electrodes can be chosen to be as large as 3 μm. Thus, the manufacture of the ink jet head can be made easier and the reliability can be improved at the same time.




Moreover, since the oscillating plates


155




a


and


155




b


are disposed further back of the inlet


153


in relation to the nozzle


154


to be slightly away from the substantial ink passage. Thus, the oscillating plates


155




a


and


155




b


do not interfere with the flow of ink in the ink passage from the inlet


153


to the nozzle


154


. This improves the high speed printing capability compared to the ink jet head


31


of the embodiment 1.




The channel plates used in the embodiment 1 and the embodiment 2 are made from silicon substrates by the wet etching method. However, the dry etching method using HF can be applied for manufacturing the channel plates as well. In that case, a channel pattern matching the mask can be formed on the etching surface irrespective of the surface orientation. As to the substrate material, photosensitive glass, ink resistant plastics such as polyimide or polysulfon can be used in addition to silicon. If a plastic material, such as polyimide and polysulfon, is used, the substrate can be made by a forming method such as molding.




Although the case of using a protection layer on the electrode has been described so far in order to prevent short circuit through ink, the protection layer is not needed if an ink with insulation properties is used.




While edge eject type ink jet heads were described in the embodiment 1 and the embodiment 2, the present invention is not limited to it, but rather it can be applied to an ink jet head of the face eject type as well as shown in the embodiment 3 below.




Embodiment 3




The ink jet head


231


shown in

FIG. 10

is of an electrostatic type using an electrostatic actuator and is different from the embodiment 1 and the embodiment 2 in terms of the nozzle constitution.




Specifically, the ink jet head


231


is of the face ejector type and includes two channels plates


250




a


and


250




b


stacked one on top of the other and has nozzles


254


on the bottom surface of the channel plate


250




b


as shown in the drawing. Members that are common to those of

FIG. 8

are assigned with the same codes and their descriptions are omitted here.




Since a large gap can be selected between the electrodes in this constitution as well, the manufacture of the ink jet head can be made easier and the reliability can be improved also.




Embodiment 4




The ink jet head


331


shown in

FIG. 11

is built into the printer. The general constitution of the ink jet printer and its operation are similar to the contents described in the embodiment 1 so that they are not repeated here. The head response of the ink jet head


331


is improved by means of increasing the drive frequency, or the frequency of applying a voltage between a pair of electrodes in case of continuous printing as described later.




As shown in the drawing, the ink jet head


331


has a multi-layered structure consisting of three elements, i.e., a channel plate


350


, a top plate


360


that covers the top of the channel plate


350


as indicated in the drawing, and a glass substrate


370


. The channel plate


350


includes ink channels


351


, an ink chamber


352


, inlets


353


, nozzles


354


, oscillating plate


355


each provided with a first electrode


356


that serves as a common electrode, and spaces


357


. The glass substrate


370


has second electrodes


372


that serves as individual electrodes formed thereon. The second electrode


372


is disposed facing and separated by spaces


357


from the first electrode


356


that is provided on the oscillating plate


355


of the channel plate


350


.




The nozzles


354


are provided on the side surface of the ink jet head


331


as indicated on the drawing. The oscillating plate


355


serves the purpose of ejecting ink through the nozzle


354


by means of causing the internal pressure change of the ink channel


351


when it deforms. The ink chamber


352


contains the ink to be supplied to the ink channel


351


. The ink stored in the ink chamber


352


is fed into the ink channel


351


through the inlet


353


.




The gap G formed by the space


357


between the first electrode


356


and the second electrode


372


is set to 0.3 μm. The first electrode


356


provided on the oscillating plate


355


consists of an impurity conductive layer formed by diffusing boron as described later.




The first electrode


356


and the second electrode


372


are connected to an ejection control unit


325


, which is the driving means for the oscillating plate, by means of wires


381


and


382


. The wire


381


connected to the first electrode


356


is grounded. The voltage from the ejection control unit


325


is applied to the second electrode


372


via the wire


382


. The oscillating plate


355


is deformed as a result of a predetermined voltage applied between the first and the second electrodes


356


and


372


.





FIG. 13

is a sectional view along the line III-III of

FIG. 12

, and

FIG. 14

is a sectional view along the line IV-IV of FIG.


12


. As shown in

FIG. 11

, FIG.


13


and

FIG. 14

, the ink jet head


331


has third electrodes


361


provided at the top plate


360


. The third electrode


361


is an individual electrode separated by the ink channel


351


and it holds a position opposing the first electrode


356


. In other words, the third electrode


361


is facing the oscillating plate


355


across a space, and is positioned relative to the first electrode


356


on the side opposite to the side the second electrode


372


is located. Therefore, the gap G between the first electrode


356


and the third electrode


361


depends on the depth of the ink channel


351


. The depth of the ink channel


351


is set to 30 μm. The third electrode


361


is connected to the ejection control unit


325


via a wire


383


. Therefore, the third electrode


361


receives a specified voltage from the ejection control unit


325


via the wire


383


.




Next, the method of manufacturing the ink jet head


331


will be described as an example.




The ink jet head


331


is manufactured using various manufacturing processes such as the semiconductor manufacturing process and the micromachine manufacturing process. It goes without saying that the present invention is applicable to an ink jet head manufactured by a method that is not described here.




First, the method of manufacturing the channel plate


350


shown in

FIG. 13

will be described referring to

FIGS. 15A

to


15


C.




A silicon substrate


390


is lapped to about 40 μm as shown in FIG.


15


A. Next, an oxide layer


396


is formed on the entire surface of the silicon substrate


390


by the thermal oxidizing method. The oxide layer


396


on the top surface (as shown in the drawing) of the silicon substrate


390


is then processed with patterning by the known photolithography and the dry etching methods to form the etching mask


396




a


shown in FIG.


15


B. The etching mask


396




a


has openings for defining the shapes of the ink channels


351


, ink chamber


352


, inlets


353


, and nozzles


354


.




Next, the silicon substrate


390


having the etching mask


396




a


formed by patterning the oxide layer


396


is etched anisotropically with KOH solution. The surface orientation of the silicon substrate


390


is (1, 1, 0) or (1, 0, 0). The anisotropic etching performed with the KOH solution stops automatically when the (1, 1, 1) surface of the silicon substrate is exposed. Therefore, by adjusting the size of the openings that become the nozzles


354


and inlets


353


to form the etching mask


396




a,


it is possible to control the etching depths in opening areas to desired values. Also, the sizes of the openings that are to be the ink channels


351


and inlets


353


as well as the etching time are adjusted in order to make the depth of the areas that form oscillating plates


355


be about 6.5 μm. The etching by the KOH solution forms properly tapered surfaces on the side walls of the ink channel


351


and ink chamber


352


by exposing the (1, 1, 1) surface.




Next, the etching mask


396




a


formed by the oxide layer


396


is removed. As a result, the ink channels


351


, ink chamber


352


, inlets


353


, and nozzles


354


are formed on the silicon substrate


390


as shown in FIG.


15


C. The channel plate


350


thus produced has a plurality of ink channels


351


and a plurality of nozzles


354


, so that an ink jet head ejects a plurality of ink drops simultaneously.




Next, the space


357


is formed on the backside of the silicon substrate


390


to produce a 0.3 μm gap G between the electrodes using a method similar to the method described above. Thus, the oscillating plate


355


shown in

FIG. 13

, etc., is formed on the silicon substrate


390


.




A resist pattern is formed on the silicon substrate


390


by the photolithography method. The resist pattern has openings for the oscillating plate


355


and the lead line that electrically connect the first electrode


356


formed on the oscillating plates


355


and the wires


381


that connect to the ejection control unit


325


. Next, boron is implanted into the opening areas for the oscillating plate


355


and the lead lines. As a result, the impurity diffusion layer that becomes the first electrode


356


and the lead lines is formed as shown in FIG.


13


. After that, an oxide layer is formed on the entire surface of the silicon substrate


390


by a thermal oxidation process. Specifically, the insulation layer is formed on the surface of the oscillating plate


355


that is located on the backside of the silicon substrate. This insulation layer is formed to prevent the short circuit between the first electrode


356


and the second electrode


372


.




Next, the formation of the glass substrate


370


where the second electrode


372


is formed will be described.




First, an ITO layer (indium oxide layer containing tin) is formed on the glass substrate


370


. The portion where the ITO layer is formed consists of an area where it faces the oscillating plate


355


of the channel plate


350


and the area adjacent to it when they are joined as shown in FIG.


13


. In addition, a boro-silicated glass substrate is used as the glass substrate


370


. Consequently, the second electrode


372


and the lead line that connect the second electrode


372


and the wire


382


are formed on the glass substrate


370


. In case of an ink jet head that has a plurality of ink channels and a plurality of nozzles, the second electrode and the lead line are formed for each ink channel.




Next, a protection layer such as a SiFH layer or a SiO


2


layer is formed covering the entire surface of the side where the second electrode


372


is formed to a thickness of about 1 μm. This protection layer is to prevent the deterioration of the drive electrode due to the ambient humidity. Therefore, the protection layer is not patterned but rather covers the entire surface of the glass substrate


370


.




The depth of the space


357


is selected in such a way that the gap G, or the distance between the first electrode


356


(insulation layer surface) and the second electrode


372


(SiFH layer surface) to be formed is to be 0.1 to 1 μm, or more preferably 0.1 to 0.5 μm in terms of a lower drive voltage. In case of this embodiment, the gap G between the electrodes is chosen to be 0.3 μm as mentioned before.




The space


357


is formed by digging the area of the oscillating plate


355


of the silicon substrate


390


that constitutes the channel plate


350


from the backside (bottom side in the drawing) by etching. However, the space


357


can be formed in the glass substrate


370


alternatively. Specifically, it is possible to form the space


357


by forming a recess with a specified depth in the area of the glass substrate


370


where it faces the oscillating plate


355


of the channel plate


350


when they are joined together as shown in FIG.


13


.




Next, the formation of the top plate


360


will be described.




The top plate


360


consists of a boro-silicated substrate as in the case of the glass substrate


370


where the second substrate


372


is provided. An ink supply port


362


for introducing ink from the ink cassette disposed above into the ink chamber


352


is formed in the top plate


360


. Next, the ITO layer is formed on the bottom surface of the top plate


360


in the area that faces the oscillating plate


355


of the channel plate


350


and in the specified area adjacent to it. In consequence, the third electrode


361


and the lead line that connects the third electrode


361


and the wire


383


are formed on the bottom side of the glass substrate


360


. In case of an ink jet head that has a plurality of ink channels and a plurality of nozzles as shown in

FIG. 11

, the third electrode and the leads line are formed for each ink channel.




The ink channel plate


350


, the glass substrate


370


and the top plate


360


manufactured as above are joined by the anode joint method as shown in FIG.


11


. The lead line as the impurity diffusion layer formed on the oscillating plate


355


of the channel plate


350


, the lead line formed on the glass substrate


370


and the lead line formed on the top plate


360


are connected to the wires


381


,


382


and


383


respectively to complete the manufacture of the ink jet head.




Next, the inks as used will be described.




As shown in the following Table, four types of ink, i.e., black (K), yellow (Y), magenta (M), and cyan (C) were used. These inks were color adjusted with dyes. However, the inks may be adjusted with pigments instead of dyes.














TABLE













Color















Composition




K




Y




M




C


















Distilled water




82.5




82.5




82.5




82.5






Dye




4.6




2.5




2.5




3.0







B/BK-SP




B/CA-Y




F/R-




B/CY-BG







(Bayer)




(Bayer)




FF3282




(Bayer)









(BASF)






Diethylene glycol




3.0




3.0




3.0




3.0






Glycerin




5.3




6.6




7.4




6.9






Triethylene




4.0




4.0




4.0




4.0






glycol






monobutyl ether






Surfactant:




0.2




1.o




0.2




0.2






Olefin E1010






(Nissin Chemical






Ind. Ltd.)






pH adjuster:




0.2




0.2




0.2




0.2






NaHCO


3








Stabilizer:




0.2




0.2




0.2




0.2






Triethanol amine











(Unit: weight %)













Next, the controller of the ink jet printer will be described referring to FIG.


16


.




The controller of the ink jet printer includes a CPU


321


, a RAM


322


, a ROM


323


, a data receiving unit


324


, an ejection control unit


325


, a head motion control unit


326


, a feed control unit


327


, a recovery system control unit


328


, and various sensors


329


. The data receiving unit


324


is connected to a machine such as a host computer and receives image data to be recorded.




The CPU


321


that controls the entire system uses the RAM


322


as needed to execute a program recorded in the ROM


323


. The program has a routine for recording the image on the sheet, and a routine for restoring the nozzle surface of the head unit to a good condition. Specifically, the former routine controls the ejection control unit


325


, the head motion control unit


326


, the feed control unit


327


, and various sensors


329


based on the image data inputted via the data receiving unit


324


and the latter routine controls the recovery system control unit


328


as needed by processing the information from various sensors


329


.




The ejection control unit


325


is controlled by the CPU


321


to drive the ink jet head


331


in the head unit. More specifically, the pulse voltage that corresponds to the image data is applied to the second electrode and the third electrode in specified timings by the ejection control unit


325


. Incidentally, the ejection control unit


325


includes a delay circuit, a charge/discharge circuit, a reverse circuit, and a reverse amplifying circuit.




The head motion control unit


326


is controlled by the CPU


321


to drive the motor that moves the carriage that carries the head unit. The feed control unit


327


is controlled by the CPU


321


to drive the sheet feed roller. Moreover, the recovery system control unit


328


is controlled by the CPU


321


to drive the motor and other things that are needed to restore the nozzle surface of the head unit to a good condition.




Next, the action of the ink jet head, or the action of the oscillating plate


355


during the ejection of an ink drop will be described referring to FIG.


17


A and FIG.


17


B.




As the first step in ejecting an ink drop, a drive voltage is applied between the first electrode


356


and the second electrode


372


. The oscillating plate


355


is attracted to the second electrode


372


due to an electrostatic force generated by the drive voltage applied as shown in FIG.


17


A. This causes the oscillating plate


355


to warp toward the second electrode


372


as shown with the two-dot chain lines in the drawing. The ink in the ink chamber


352


flows through the inlet


353


into the ink channel


351


. The first electrode


356


formed on the oscillating plate


355


is grounded. Therefore, the positive voltage, e.g., a 30 V drive voltage is applied to the second electrode (drive electrode)


372


. This drive voltage generates the force F


1


to be applied to the oscillating plate


355


as shown in the drawing.




The drive voltage is held for a predetermined time, e.g., several microseconds to tens microseconds by various circuits in the ejection control unit


325


. Subsequently, the drive voltage is cut off and an auxiliary voltage is applied between the first electrode


356


and the third electrode


361


within a predetermined time. Since the first electrode


356


formed in the oscillating plate


355


is grounded, the positive voltage, e.g., 300V, is applied to the third electrode


361


.




In order to apply a voltage effectively minimizing the waste of energy, the time is preferably 0.1 to 10 microseconds. The reason is as follows: If the predetermined time is chosen to be less than 0.1 microsecond, the predetermined time is shorter than the time required for the oscillating plate


355


to restore back to the restoration position, or the original position, although it depends on the deformation due to the drive voltage. Therefore, the tensile force is developed during the restoration of the oscillating plate


355


, which causes an energy loss. In other words, the loss is less if the tensile force is provided after the restoration. On the other hand, if the predetermined time is chosen to be longer than 10 microseconds, the predetermined time is longer than the time required for the oscillating plate


355


to pass the original position and oscillate one cycle, although it depends on the deformation due to the drive voltage. Therefore, the tensile force is developed at the timing when it returns to the original position after one oscillation. This also causes energy loss and is not desirable.




Thus, the oscillating plate


355


that has been attracted toward the second electrode


372


due to the application of the drive voltage returns to the original position on account of the restoration force of the oscillating plate


355


itself after the drive voltage cut-off. At about the same instant, a force F


2


is applied to the oscillating plate


355


due to the application of the auxiliary voltage as shown in FIG.


17


B. Therefore, the oscillating plate


355


is pulled rapidly away from the second electrode


372


.




The volume of the ink channel


351


contracts sharply and develops a pressure. As a result, the ink which has filled the ink channel


351


flies out as a drop from the nozzle


354


and lands on the sheet


2


to form a specified image.




In the embodiment 4, the third electrode


361


is positioned relative to the first electrode


356


on the side opposite to the side the second electrode


372


is located, the oscillating plate


355


is pulled toward the second electrode


372


when the drive voltage is applied between the first electrode


356


and the second electrode


372


, and the auxiliary voltage is applied between the first electrode


356


and the third electrode


361


when the oscillating plate


355


returns to the original position by its own restoring force.




With this constitution, the restoring force of the oscillating plate


355


is enhanced since the oscillating plate


355


is pulled forcibly away from the second electrode


372


by means of an electrostatic force. This causes the oscillating plate


355


return to its original position quicker than when it depends on the restoring force of the oscillating plate


355


alone. In other words, the tracking capability of the mechanical constitution including the oscillating plate is improved and thus the drive frequency of the ink jet head can be increased. This means that the preparation for the next printing can be done quicker so that the head response can be improved to enable high speed printing.




The ejecting speed of the ink drop ejected from the nozzle


354


was 8 meters per second when the third electrode


361


was not provided. On the contrary, the ejecting speed was increased to 10 meters per second as a result of the enlargement of the restoring force of the oscillating plate


355


when the third electrode


361


was provided. This will prevent the misplacement of the ink drop on its landing on the recording medium, which otherwise may be caused by the time lag between the ejection and the landing on the recording medium. Since the fluctuation of the ink drop flight is reduced, the image distortion is minimized and the better image recording is accomplished.




It is obvious that this invention is not limited to the particular embodiments shown and described above but may be variously changed and modified by any person of ordinary skill in the art without departing from the technical concept of this invention.




In the embodiment 4, as shown in

FIG. 11

, a case of forming the third electrode


361


and the lead line individually for each ink channel


351


was described. However, the present invention is not limited to such a constitution. For example, the lead lines of a plurality of third electrodes


361


can be connected to form a single common electrode so that the auxiliary voltage can be applied to the common electrode. With such a constitution, it is possible to reduce the manufacturing cost because the constitution of each circuit in the ejection control unit


325


is simplified.



Claims
  • 1. An electrostatic ink jet head having a set of elements comprising:an ink channel that communicates with a nozzle that ejects ink; a pair of non-piezoelectric oscillating plates that are disposed opposing to each other on walls of said ink channel; and a pair of electrodes provided in contact with said non-piezoelectric oscillating plates, respectively, wherein a voltage is applied between said electrodes.
  • 2. An electrostatic ink jet head in accordance with claim 1, wherein said ink is ejected by applying a voltage between said electrodes.
  • 3. An electrostatic ink jet head in accordance with claim 1, wherein a plurality of the sets of elements are arranged.
  • 4. An electrostatic ink jet head in accordance with claim 4, wherein one of said electrodes is used as a common electrode.
  • 5. An ink jet head comprising:an ink channel that communicates with a nozzle that ejects ink; a pair of oscillating plates that are disposed opposing to each other on walls of said ink channel; and a pair of electrodes provided in contact with said oscillating plates, respectively; wherein a voltage is applied between said electrodes; and wherein said electrodes are disposed respectively on an inside of said oscillating plates provided opposing to each other.
  • 6. An electrostatic ink jet recording apparatus having a set of elements comprising:an ink channel that communicates with a nozzle that ejects ink; a pair of non-piezoelectric oscillating plates that are disposed opposing to each other on walls of said ink channel; a pair of electrodes disposed in contact with said non-piezoelectric oscillating plates, respectively; and a controller for controlling a voltage to be applied between said electrodes.
  • 7. An electrostatic ink jet recording apparatus in accordance with claim 6, wherein ink is ejected by applying a voltage between said electrodes.
  • 8. An electrostatic ink jet recording apparatus in accordance with claim 6, wherein a plurality of the sets of elements are provided.
  • 9. An electrostatic ink jet recording apparatus in accordance with claim 6, wherein one of said electrodes is used as a common electrode.
  • 10. An electrostatic ink jet recording apparatus in accordance with claim 6, wherein said controller discharges electric charges of said electrodes.
  • 11. An ink jet recording apparatus comprising:an ink channel that communicates with a nozzle that ejects ink; a pair of oscillating plates that are disposed opposing to each other on walls of said ink channel; a pair of electrodes disposed in contact with said oscillating plates, respectively; and a controller for controlling a voltage to be applied between said electrodes; wherein a plurality of sets of said composing elements are provided; and wherein said electrodes are disposed respectively on an inside of said oscillating plates provided opposing to each other.
  • 12. An ink jet recording apparatus comprising:an ink channel that communicates with a nozzle that ejects ink; a pair of oscillating plates that are disposed opposing to each other on walls of said ink channel; a pair of electrodes disposed in contact with said oscillating plates, respectively; and a controller for controlling a voltage to be applied between said electrodes; wherein relative dielectric constant of ink to be filled in said ink channel is larger than 1.
  • 13. An ink jet head comprising:an ink channel that communicates with a nozzle that ejects ink; an oscillating plate that is disposed facing said ink channel; a first electrode disposed on said oscillating plate, a side where said first electrode is disposed being opposite to a side that faces said ink channel; a second electrode that is disposed opposing said first electrode; and a third electrode located relative to said first electrode on a side opposite to a side said second electrode is located.
  • 14. An ink jet head in accordance with claim 13, wherein said third electrode is opposing said oscillating plate across said ink channel.
  • 15. An ink jet head in accordance with claim 13, wherein said second electrode is separated from said first electrode by a space.
  • 16. An ink jet recording apparatus comprising:an ink channel that communicates with a nozzle that ejects ink; an oscillating plate that is disposed facing said ink channel; a first electrode disposed on said oscillating plate, a side where said first electrode is disposed being opposite to a side that faces said ink channel; a second electrode that is disposed opposing said first electrode; a third electrode located relative to said first electrode on a side opposite to a side said second electrode is located; and a controller for controlling application of voltages to said electrodes.
  • 17. An ink jet recording apparatus in accordance with claim 16, wherein said third electrode is opposing said oscillating plate across said ink channel.
  • 18. An ink jet recording apparatus in accordance with claim 16, wherein said controller applies a voltage between said first and third electrodes within a predetermined time after stopping application of a voltage between said first and second electrodes.
  • 19. An ink jet recording apparatus in accordance with claim 18, wherein said predetermined time is 0.1 to 10 microseconds.
  • 20. An ink jet recording apparatus in accordance with claim 16, wherein said voltage applied between said first and second electrodes is different from said voltage applied between said first and third electrodes.
  • 21. A method for driving an ink jet head comprising an oscillating plate that is disposed facing an ink channel, a first electrode disposed on said oscillating plate, a side where said first electrode is disposed being opposite to a side that faces said ink channel, a second electrode that is disposed opposing said first electrode, and a third electrode located relative to said first electrode on a side opposite to a side said second electrode is located, said method comprising the steps of:a first voltage application step that applies a voltage between said first and second electrodes; and a second voltage application step that applies a voltage between said first and third electrodes.
  • 22. A method in accordance with claim 21, wherein said second voltage application step is executed after a predetermined time after said first voltage application step is stopped.
  • 23. A method in accordance with claim 22, wherein said predetermined time is 0.1 to 10 microseconds.
  • 24. A method in accordance with claim 21, wherein said voltage used in said first voltage application step is different from said voltage used in said second voltage application step.
  • 25. An electrostatic ink jet head comprising:an ink channel that is defined by a plurality of surfaces that include a first surface and a second surface opposing to said first surface through said ink channel, said first surface being a main surface of a non-piezoelectric oscillating plate, said ink channel communicating with a nozzle for ejecting ink therefrom; a first electrode provided at a position corresponding to the first surface; and a second electrode provided at a position corresponding to the second surface; wherein an electrical field can be generated between said first and second electrodes by applying an electrical voltage therebetween.
  • 26. An electrostatic ink jet head as claimed in claim 25 wherein one of said electrodes is a common electrode.
Priority Claims (2)
Number Date Country Kind
10-119435 Apr 1998 JP
10-119436 Apr 1998 JP
US Referenced Citations (1)
Number Name Date Kind
4228440 Horike et al. Oct 1980
Foreign Referenced Citations (1)
Number Date Country
5-050601 Mar 1993 JP