Piezo-electric actuator of ink jet printer head and method for producing same

Information

  • Patent Grant
  • 6575565
  • Patent Number
    6,575,565
  • Date Filed
    Wednesday, September 27, 2000
    24 years ago
  • Date Issued
    Tuesday, June 10, 2003
    21 years ago
Abstract
An actuator for the print head of an ink jet printer is fitted to the ink channels of the head. The actuator includes an active layer and a restraining layer. One side of the active layer faces the ink channels. The active layer can deform with a drive voltage applied to it. The restraining layer is provided on the other side of the active layer, and cannot be activated with a drive voltage. The restraining layer restrains the active layer from deforming. It is possible to integrally form the active and restraining layers by stacking green sheets and calcining the stacked sheets at the same time. This makes it possible to provide an actuator simple in structure and low-cost.
Description




BACKGROUND OF THE INVENTION




1. Field of the Invention




The present invention relates to the piezo-electric actuator of the print head of an ink jet printer and a method for producing such an actuator.




2. Description of Related Art




The print head of a known ink jet printer has ink channels and piezo-electric elements provided adjacently to them. The ink jet printer performs printing a print by applying a voltage to the piezo-electric elements to reduce the volume of one or more of the ink channels, ejecting ink from this channel or these channels through an orifice or orifices.





FIG. 11

of the accompanying drawings shows the print head of a conventional ink jet printer, which is disclosed in the Assignee's U.S. Pat. No. 5,402,159, for example. This print head includes a piezo-electric actuator


103


, which is provided over ink ejectors


90




a


,


90




b


and


90




c


. The piezo-electric actuator


103


includes five piezo-electric ceramic sheets or layers


40


laminated or stacked together. An internal negative electrode


42


lies on the upper side of each of the top, middle and bottom ceramic sheets


40


. Separate internal positive electrodes


44




a


,


44




b


and


44




c


lie on the upper side of each of the other two ceramic sheets


40


. The positive electrodes


44




a


,


44




b


and


44




c


are provided over or above the ink ejectors


90




a


,


90




b


and


90




c


, respectively. The ink ejectors


90




a


,


90




b


and


90




c


have ink channels


32




a


,


32




b


and


32




c


, respectively, and orifices


37




a


,


37




b


and


37




c


, respectively. This print head consists of a small number of parts and is simple in structure. It is easy to make the resolution of the print head higher by varying the electrode pattern. The use of the laminated piezo-electric actuator


103


results in lower drive voltage.




A deformation restraining member


80


is bonded to restrain the piezo-electric actuator


103


from deforming away from the ink channels


32




a-




32




c


. This makes it possible to deform the piezo-electric actuator


103


effectively toward the ink channels


32




a-




32




c


and consequently drive the ink ejectors


90




a-




90




c


at lower voltage. This also makes it possible to reduce the cross talk at each ink channel


32




a


,


32




b


or


32




c


which is caused by the deformation of the adjacent ink channel or channels due to irregular deformation of the piezo-electric actuator


103


. The cross talk reduction improves the SN ratio (S/N).




The process for producing this print head includes alternately stacking, pressing and calcining the piezo-electric ceramic sheets


40


and the internal electrodes


42


and


44




a-




44




c


, and thereafter bonding the deformation restraining member


80


with an adhesive or the like. This complicates the process, increases the number of steps of the process, and raises the production cost.




SUMMARY OF THE INVENTION




In view of the foregoing problems, it is an object of the present invention to provide a piezo-electric actuator for an ink jet printer head which makes it possible to reduce cross talk, restrain the laminated piezo-electric element of the print head from deforming away from the ink channels of the head, and which can be assembled simply and produced at a low cost. It is another object to provide a method for producing such an actuator.




In accordance with a first aspect of the present invention, a piezo-electric actuator is provided for an ink jet printer head which has an ink channel and an orifice, and which ejects ink from the channel through the orifice by changing the volume of the channel. The actuator includes an active layer and a restraining layer. One side of the active layer faces the ink channel. The active layer includes at least one sheet formed out of piezo-electric material and provided with an electrode thereon. The restraining layer is positioned on the other side of the active layer, and restrains the active layer from deforming. The restraining layer includes at least one sheet. The active and restraining layers are sintered to be integral with each other.




The active layer is interposed between the ink channel and the restraining layer, which is formed integrally with the active layer. The restraining layer restrains the active layer from deforming. This makes it possible to efficiently utilize the deformation of the active layer to change the volume of the ink channel. It is therefore possible to improve the ink ejecting performance of the print head and reduce power consumption. This also makes it possible to prevent deformation in parallel to the layers to restrain the volume change of the ink channel or channels adjacent to a driven ink channel. It is therefore possible to prevent cross talk.




The active and restraining layers are formed by being integrally sintered. Consequently, in comparison with the case where a deformation restraining member is bonded with an adhesive or the like, it is possible to reduce the number of steps of the process for producing the piezo-electric actuator. This simplifies the producing process and lowers the production cost. It is also possible to increases the strength of the actuator.




The sheets of the active and restraining layers may be formed out of the same material. In this case, members for forming the active layer can be used as they are for the restraining layer. This makes it possible to produce the piezo-electric actuator simply at a lower cost. The same material makes the layers fit together, and prevents them from being warped, distorted or deformed, when they are integrally sintered. This results in high accuracy or precision.




The sheet of the restraining layer may be provided with a dummy electrode, which does not contribute to the deformation for driving the ink channel. In this case, when the active and restraining layers are integrally sintered, it is possible to equalize the differences in shrinking percentage in the directions perpendicular to the layers to prevent warps and/or waves due to the difference in shrinking percentage between the layers. This can made the piezo-electric actuator very flat. Consequently, the actuator can be bonded closely to the cavity layer in which the ink channel is formed. This results in high accuracy or precision.




The dummy electrode of the restraining layer may be connected to the electrode of the active layer, and face this electrode through a ceramic, which is a dielectric. In this case, there is no potential difference between the dummy electrode and the electrode of the active layer, producing no electric capacity between them. As a result, no electric power is wasted.




The dummy electrode of the restraining layer and the electrode of the active layer may be positioned in substantial symmetry in the piezo-electric actuator. In this case, when the active and restraining layers are integrally sintered, it is possible to roughly equalize the differences in shrinking percentage in the directions perpendicular to the layers to prevent warps and/or waves due to the difference in shrinking percentage between the layers. This can make the piezo-electric actuator even flatter. Consequently, the actuator can be bonded closely to the cavity layer. This results in high accuracy or precision.




In accordance with a second aspect of the present invention, a piezo-electric actuator is provided for an ink jet printer head. The actuator includes a laminate including a plurality of piezo-electric sheets stacked and sintered at the same time. The actuator also includes an electrode formed on at least one of the sheets which is positioned on one side of the laminate. Only said at least one sheet on the one side is adapted for activation with a drive voltage. At least one of the sheets which is positioned on the other side of the laminate is not adapted for activation (deactivated). This actuator is simple in structure and therefore very easy to produce.




In accordance with a third aspect of the present invention, a print head is provided for an ink jet printer. This print head includes an ink ejector having an ink channel formed therein and an orifice through which ink can be ejected from the channel. The print head also includes a piezo-electric actuator for changing the volume of the ink channel. The actuator includes an active layer and a restraining layer. One side of the active layer faces the ink channel. The active layer includes at least one sheet formed out of piezo-electric material and provided with an electrode thereon. The restraining layer is positioned on the other side of the active layer, and restrains the active layer from deforming. The restraining layer includes at least one sheet. The active and restraining layers are sintered to be integral with each other. The print head includes a piezo-electric actuator according to the invention, and is therefore highly reliable and low-cost.




In accordance with a fourth aspect of the present invention, a method is provided for producing a piezo-electric actuator for an ink jet printer head. The method comprises the steps of:




providing at least one first green sheet having an electrode pattern, the first green sheet being formed out of piezo-electric material and forming an active layer of the actuator;




laying at least one second green sheet on the first green sheet, the second green sheet forming a restraining layer of the actuator; and




calcining the first and second green sheets at the same time to be integral with each other.




This producing method involves forming the active layer and the restraining layer by calcining them. The restraining layer restrains the active layer from deforming away from the ink channels of the print head. It is therefore possible to efficiently utilize the deformation of the active layer to change the volume of the ink channels. This makes it possible to improve the ink ejecting performance of the print head and reduce power consumption. It is also possible to prevent the horizontal or lateral deformation of the active layer to restrain the volume change of the ink channel or channels adjacent to a driven ink channel, preventing cross talk. In particular, the active and restraining layers are formed by being integrally sintered. Accordingly, in comparison with the case where a deformation restraining member is stuck with an adhesive or the like, the piezo-electric actuator can be produced at a low cost by a simple process including a reduced number of steps, and its strength can be high.




The second green sheet, too, may be formed out of the piezo-electric material. A plurality of first green sheets and a plurality of second green sheets may be provided. The producing method may further comprise the step of providing at least part of the second green sheets with a dummy electrode or dummy electrodes. The second green sheets may include a sheet provided with a dummy electrode and a sheet provided with no dummy electrode. In this case, the restraining layer includes a sheet provided with a dummy electrode, which does not contribute to deformation, and a sheet provided with no dummy electrode. Therefore, when the active and restraining layers are integrally sintered, it is possible to equalize in balance the differences in shrinking percentage in the directions perpendicular to the layers to prevent warps and/or waves due to the difference in shrinking percentage between the layers. This can made the piezo-electric actuator very flat.




The second green sheet without a dummy electrode may be laid on the second green sheet provided with a dummy electrode. In this case, the restraining layer includes a sheet having no dummy electrode and laid on a sheet provided with a dummy electrode, which does not contribute to deformation. Therefore, when the active and restraining layers are integrally sintered, the dummy electrode can restrain the electrode pattern on the active layer from diffusing, and it is possible to equalize in balance the differences in shrinking percentage to prevent warps, making the piezo-electric actuator very flat.




The producing method may further comprise the steps of pressing with heat and then degreasing the first and second green sheets before calcining them.











BRIEF DESCRIPTION OF THE DRAWINGS





FIG. 1

is a vertical cross section of main parts of the print head of an ink jet printer embodying the present invention.





FIG. 2

is an electric connection or wiring diagram of the piezo-electric actuator of the print head.





FIG. 3

is a graph of the relationship between the number of sheets of the restraining layers of the piezo-electric actuator of a print head and the change in sectional area of ink channel of the head.





FIG. 4

is an exploded perspective view of the piezo-electric actuator.





FIG. 5

is an exploded perspective view of the main parts of the print head.





FIG. 6

is a perspective view of main parts of the ink jet printer.





FIG. 7

is a vertical cross section of main parts of a modified print head according to the present invention.





FIG. 8

is a vertical cross section of main parts of another modified print head according to the present invention.





FIG. 9

is a vertical cross section of main parts of still another modified print head according to the present invention.





FIG. 10

is a vertical cross section of main parts of yet another modified print head according to the present invention.





FIG. 11

is a vertical cross section of main parts of the print head of a conventional ink jet printer.











DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS





FIGS. 1-6

show a preferred embodiment of the present invention. The parts and/or components of the embodiment which are identical and/or equivalent to the counterparts of the prior art are assigned the same reference numerals without being described.




With reference to

FIG. 6

, an ink jet printer


1


includes a horizontal platen


10


for feeding printing paper


11


perpendicularly to its axis. The platen


10


includes a shaft


12


, which is supported rotatably by a frame


13


, and can be rotated by a motor


14


through a drive gear train.




A pair of guide rods


20


(


20




a


and


20




b


) extend below the platen


10


and in parallel to its shaft


12


, and are fixed to the frame


13


. The guide rods


20


slidably support a carriage


18


, which is connected to a timing belt


24


. The timing belt


24


extends between a driven pulley


21


and a driving pulley


22


, which can be rotated by a motor


23


to drive the timing belt


24


. The carriage


18


supports a print head


15


and an ink supply device


16


on it. Thus, the timing belt


24


can slide the carriage


18


on the guide rods


20


along the platen


10


, with the print head


15


facing the platen


10


.




With reference to

FIG. 1

, the print head


15


(

FIG. 6

) includes a cavity layer


30


and a piezo-electric actuator


3


, which consists of an active layer


38


and a restraining layer


70


. The cavity layer


30


has three ink channels


32




a


,


32




b


and


32




c


formed in it and each having an open top. The cavity layer


30


also has three orifices


37




a


,


37




b


and


37




c


formed through its bottom and communicating with the ink channels


32




a


,


32




b


and


32




c


, respectively. The active layer


38


lies on the top of the cavity layer


30


. The active layer


38


includes six piezo-electric ceramic sheets


40




a


,


40




b


,


40




c


,


40




d


,


40




e


and


40




f


laminated or stacked together and each having an electrode pattern formed on their upper sides. The piezo-electric ceramic sheets


40




a-




40




f


each have an electrostrictive strain effect. The electrostrictive strain effect of the active layer


38


changes the volume of the ink channels


32




a


,


32




b


and


32




c


to eject through the orifices


37




a


,


37




b


and


37




c


, respectively, the ink stored in these channels. The restraining layer


70


lies on the top of the active layer


38


and is formed integrally with the active layer. The restraining layer


70


includes three ceramic sheets


71




a


,


71




b


and


71




c


laminated or stacked together. The restraining layer


70


restrains the active layer


38


from deforming upward when the active layer is driven. The restraining layer


70


makes the whole actuator


3


more rigid to prevent cross talk.




As shown in

FIG. 5

, the cavity layer


30


includes a channel body


34


and an orifice plate


36


, which covers the bottom of the channel body. The orifices


37




a-




37




c


are formed through the orifice plate


36


. The channel body


34


is a rectangular parallelepiped, in which the ink channels


32




a


,


32




b


and


32




c


are formed in parallel and spaced at regular intervals. Each of the ink channels


32




a-




32




c


has a width of about 250 microns and a height of 60 microns. The channel body


34


and the orifice plate


36


are made of irony material and bonded together. Otherwise, the channel body


34


and orifice plate


36


might be integrally molded by calcining ceramics or the like, or injection-molding alumina or similar material.




Each of the ink channels


32




a-




32




c


is filled always with ink by being supplied through a supply passage (not shown) communicating with the ink supply device


16


(FIG.


6


). A negative pressure is applied to the ink in the ink channels


32




a-




32




c


so that the surface tension of ink produces concave menisci of ink in the orifices


37




a-




37




c


. This normally prevents ink from leaking through the orifices


37




a-




37




c


, but allows ink to be ejected through them only when the internal pressure in the ink channels


32




a


,


32




b


and


32




c


rises. Each ink supply passage is fitted with a check valve (not shown) for preventing ink from flowing back to the ink supply device


16


when the internal pressure in the associated ink channel rises.




The orifices


37




a-




37




c


might be replaced by nozzles extending from the respective ink channels


32




a-




32




c


. The nozzles could be angled to adjust the direction of ejection from the ink channels


32




a-




32




c


. The orifices


37




a-




37




c


might be positioned elsewhere than the bottoms of the ink channels


32




a-




32




c.






As best shown in

FIG. 4

, each of the three piezo-electric ceramic sheets


40




a


,


40




c


and


40




e


of the active layer


38


has an internal negative electrode


42


and a connector


43


which are formed on its upper side as stated later on. The connector


43


connects the negative electrode


42


electrically to the outside. The negative electrode


42


covers the substantial portion except a peripheral portion of the upper side of the associated piezo-electric ceramic sheet


40




a


,


40




c


or


40




e.






Likewise, each of the other three piezo-electric ceramic sheets


40




b


,


40




d


and


40




f


of the active layer


38


has three internal positive electrodes


44




a


,


44




b


and


44




c


and three connectors


45




a


,


45




b


and


45




c


formed on its upper side. The connectors


45




a


,


45




b


and


45




c


electrically connect the positive electrodes


44




a


,


44




b


and


44




c


, respectively, to the outside. The positive electrodes


44




a


,


44




b


and


44




c


are associated with the ink channels


32




a


,


32




b


and


32




c


(FIG.


5


), respectively, and extend in parallel. Each of the positive electrodes


44




a-




44




c


takes the form of a belt or band and has a width of about 120 microns.




The internal negative and positive electrodes


42


and


44




a-




44




c


are made of Ag—Pd metallic material and each have a thickness of about 2 microns. The piezo-electric ceramic sheets


40




a-




40




f


with the two types of electrode patterns printed on them are alternately laminated or stacked.




Thus, as shown in

FIG. 1

, one internal negative electrode


42


is positioned on one side of each of the five piezo-electric ceramic sheets


40




a-




40




e


, while three internal positive electrodes


44




a-




44




c


are positioned on the other side of each of these sheets and one side of the bottom piezo-electric ceramic sheet


40




f


. Each of the six piezo-electric ceramic sheets


40




a-




40




f


consists of piezo-electrically active portions


46




a


,


46




b


and


46




c


and piezo-electrically inactive portions


48


. Each of the active portions


46




a-




46




c


of the five sheets


40




a-




40




e


is formed between the adjacent negative electrode


42


and one of the adjacent positive electrodes


44




a-




44




c


, each of which takes the form of a belt or band. Each of the active portions


46




a-




46




c


of the bottom sheet


40




f


is formed under one of the adjacent positive electrodes


44




a-




44




c


. Each of the active portions


46




a-




46




c


has a width of about 120 microns. The other portions of the six piezo-electric ceramic sheets


40




a-




40




f


are the inactive portions


48


. When voltage is applied between the positive electrodes


44




a


,


44




b


or


44




c


and the negative electrodes


42


, electric fields are generated in the associated active portions


46




a


,


46




b


or


46




c


, which then deform vertically due to the electrostrictive strain effect, while no electric field is generated in the inactive portions


48


, which do not deform. The channel body


34


is fixed to the bottom of the active layer


38


in such a manner that the active portions


46




a


,


46




b


and


46




c


are positioned over or above the ink channels


32




a


,


32




b


and


32




c


, respectively.




The restraining layer


70


includes three ceramic sheets


71




a


,


71




b


and


71




c


, which are identical in structure and material and equal in size to the piezo-electric ceramic sheets


40




a-




40




f


of the active layer


38


. As shown in

FIGS. 1

,


2


and


4


, each of the top and bottom ceramic sheets


71




a


and


71




c


of the restraining layer


70


has three dummy positive electrodes


73




a


,


73




b


and


73




c


and three connectors


75




a


,


75




b


and


75




c


, which are identical in structure to the internal positive electrodes


44




a


,


44




b


and


44




c


and the connectors


45




a


,


45




b


and


45




c


, respectively, on the piezo-electric ceramic sheets


40




b


,


40




d


and


40




f


. The middle ceramic sheet


71




b


of the restraining layer


70


has a dummy negative electrode


72


and a connector


74


, which are identical in structure to the internal negative electrodes


42


and the connectors


43


, respectively, on the piezo-electric ceramic sheets


40




a


,


40




c


and


40




e.






The six piezo-electric ceramic sheets


40




a-




40




f


and the three ceramic sheets


71




a-




71




c


are comprised of green sheets


50


and


51


(FIG.


4


), on which electrodes etc. are printed as stated above. The green sheets


50


and


51


can be used as common parts. After the piezo-electric actuator


3


is formed, the piezo-electric ceramic sheets


40




a-




40




f


differ from the ceramic sheets


71




a-




71




c


in location, electric wiring as described later on, and function, and therefore their names differ.




The active layer


38


and the restraining layer


70


are produced by the following method.




First, ceramic powder of ferroelectric lead zirconate titanate (PZT (PbTiO


3


.PbZrO


3


)) material, a binder and a solvent are mixed into a mixed liquid having a viscosity between 10,000 and 30,000 CPS. The mixed liquid is spread and dried on films of polyethylene terephthalate (PET) or other plastic material to form nine green sheets, each of which has a thickness between about 22.5 and 28 microns. Five of the green sheets are used as the green sheets


50


, and the other four sheets are used as the green sheets


51


. Metallic material is screen-printed on those portions of the green sheets


50


which will be the internal positive electrodes


44




a-




44




c


, the dummy positive electrodes


73




a-




73




c


and the connectors


45




a-




45




c


and


75




a-




75




c


. Likewise, metallic material is screen-printed on those portions of the green sheets


51


which will be the internal negative electrodes


42


, the dummy negative electrode


72


and the connectors


43


and


74


.




The nine green sheets


50


and


51


are alternately stacked, with one green sheet


50


positioned at the top and another green sheet


50


positioned at the bottom. In the end, the five green sheets


50


and the four green sheets


51


of just the same structure are alternately stacked as the active layer


38


and the restraining layer


70


. At this stage, the active layer


38


and the restraining layer


70


are not yet distinguished.




The stacked green sheets


50


and


51


are pressed with heat, degreased and sintered to form a piezo-electric ceramic block, which consists of the active layer


38


and restraining layer


70


. The calcination of the green sheets


50


and


51


stacked as a laminated block will be explained below.




As stated already, the piezo-electric actuator


3


consists of an active layer


38


and a restraining layer


70


. Electrodes are essential to the active layer


38


, while the restraining layer


70


functionally needs to have no electrode. When the laminated block is sintered, however, the piezo-electric ceramics differ in shrinking percentage from the metallic material for the electrodes. Even a slight difference in shrinking percentage may warp or wave the sintered active layer


38


, thereby damaging or spoiling its flatness. The non-flat active layer


38


can be bonded less closely (with lower adherence) to the cavity layer


30


. This may cause a problem that ink leaks from the ink channels


32




a-




32




c


, so that defective products may be made. This may also cause a problem that the active layer


38


needs regrinding (or needs to be ground again), so that the number of producing process steps may increase and the production costs may be higher. This may further cause a problem that gaps between the layers


38


and


30


need filling with fillers, so that the strength of the laminated block may be lower.




Therefore, as stated earlier on, the restraining layer


70


and the active layer


38


are made of the same piezo-electric ceramic material so that they are equal in shrinking percentage when the ceramics are sintered. The dummy negative electrode


72


, the connector


74


, the dummy positive electrodes


73




a-




73




c


and the connectors


75




a-




75




c


, which are formed on the ceramic sheets


71




a-




71




c


of the restraining layer


70


, are identical to the internal negative electrodes


42


, connectors


43


, internal positive electrodes


44




a-




44




c


and connectors


45




a-




45




c


, respectively, on the piezo-electric ceramic sheets


40




a-




40




f


of the active layer


38


, but do not contribute toward deforming the restraining layer


70


. Therefore, because the active layer


38


and the restraining layer


70


have the very same structure, they can be identical in shrinking percentage when they are sintered. The internal electrodes


42


,


44




a-




44




c


,


72


and


73




a-




73




c


and the connectors


43


,


45




a-




45




c


,


74


and


75




a-




75




c


of the layers


38


and


70


of the laminated block as a whole are arrayed in vertical symmetry (symmetrically in the directions of lamination). This symmetrizes the shrinking percentage of the whole laminated block so as not to warp this block being sintered.




With reference to

FIGS. 2 and 4

, the piezo-electric actuator


3


includes an external negative electrode


52




a


made of electrically conductive metallic material. This external electrode


52




a


electrically connects the connectors


43


on the three piezo-electric ceramic sheets


40




a


,


40




c


and


40




e


and the connector


74


on the ceramic sheet


71




b


. The piezo-electric actuator


3


includes another external negative electrode


52




b


made of an electrically conductive metal plate. This external electrode


52




b


electrically connects the connectors


75




a-




75




c


on the two ceramic sheets


71




a


and


71




c


. These external electrodes


52




a


and


52




b


are electrically connected. Consequently, the dummy electrodes


72


and


73




a-




73




c


on the three ceramic sheets


71




a-




71




c


and the internal negative electrodes


42


on the piezo-electric ceramic sheets


40




a


,


40




c


and


40




e


are equal in electric potential.




The piezo-electric actuator


3


also includes three external positive electrode


54




a


,


54




b


and


54




c


made of electrically conductive metallic material. The external electrode


54




a


electrically connects the connectors


45




a


on the piezo-electric ceramic sheets


40




b


,


40




d


and


40




f


. The external electrode


54




b


electrically connects the connectors


45




b


on the piezo-electric ceramic sheets


40




b


,


40




d


and


40




f


. The external electrode


54




c


electrically connects the connectors


45




c


on the piezo-electric ceramic sheets


40




b


,


40




d


and


40




f.






The external negative and positive electrodes


52




a


,


52




b


and


54




a-




54




c


are formed out of metallic material, which is printed directly on side faces of the active layer


38


and the restraining layer


70


, or with which these faces are coated directly. Alternatively, the external electrodes might be metal plates connected in contact with the connectors


43


,


74


,


75




a-




75




c


and


45




a-




45




c


, or wires soldered to these connectors. These electrodes might have other structures.




Because the dummy electrodes


72


and


73




a-




73




c


do not contribute toward deforming the ceramic sheets


71




a-




71




c


of the restraining layer


70


, it is not necessary to apply a drive voltage to these electrodes. Even if the dummy electrodes


72


and


73




a-




73




c


and the connectors


74


and


75




a-




75




c


were insulated in order not to be electrically polarized, a potential difference might be generated between them and the top internal negative electrode


42


of the active layer


38


. The potential difference produces an electric capacity, which produces an electric current. The current is so small as not to contribute toward deforming the ceramic sheets


71




a-




71




c


, but results in a power loss. In particular, if the power source for the piezo-electric actuator


3


is a battery, the power loss shortens the life of the battery. Therefore, the dummy electrodes


72


and


73




a-




73




c


and the connectors


74


and


75




a-




75




c


are connected electrically to the internal negative electrodes


42


of the active layer


38


. This prevents a potential difference being generated between the dummy electrodes


72


and


73




a-




73




c


and the connectors


74


and


75




a


-


75




c


of the restraining layer


70


and the top internal negative electrode


42


of the active layer


38


. It is consequently possible to prevent the production of a needless capacity.




The laminated block thus constructed is then immersed in an oil bath (not shown) filled with a silicone oil or another insulating oil at a temperature of about 130 degrees C. An electric field of about 2.5 kv/mm is applied between the external negative electrode


52




a


and the external positive electrodes


54




a-




54




c


to polarize the piezo-electric ceramic sheets


40




a-




40




f


of the active layer


38


.




As shown in

FIG. 2

, the external negative electrode


52




a


is grounded through a cord (not shown) to have a ground potential. The external positive electrodes


54




a


,


54




b


and


54




c


are connected through switches


62




a


,


62




b


and


62




c


, respectively, and a cord (not shown) to the positive pole of a power source


60


, the negative pole of which is grounded. When a controller (not shown) makes one or more of the switches


62




a-




62




c


closed, a drive voltage is applied between the associated internal positive electrodes


44




a


,


44




b


,


44




c


and the internal negative electrodes


42


from the power source


60


.




As shown in

FIG. 5

, the block consisting of the active layer


38


and the restraining layer


70


, and the cavity layer


30


are assembled into the print head


15


(FIG.


6


).





FIGS. 7

,


8


,


9


and


10


show modified piezo-electric actuators


203


,


303


,


403


and


503


, respectively. In

FIGS. 7-10

, parts identical to the counterparts of the piezo-electric actuator


3


are assigned the same reference numerals without being described.




With reference to

FIG. 7

, similarly to the piezo-electric actuator


3


, the modified piezo-electric actuator


203


consists of an active layer


238


and a restraining layer


270


. As shown in

FIG. 1

, the active layer


38


of the actuator


3


includes six piezo-electric ceramic sheets


40




a-




40




f


. The active layer


238


of the actuator


203


differs from the active layer


38


in including four piezo-electric ceramic sheets


40


. The restraining layer


270


includes five ceramic sheets


71


, on each of which a dummy negative electrode


72


is formed. Each dummy negative electrode


72


is grounded through a ground electrode. As shown in

FIG. 4

, the restraining layer


70


of the actuator


3


is comprised of two green sheets


50


and one green sheet


51


, which are alternately stacked and sintered. As shown in

FIG. 7

, the restraining layer


270


of the actuator


203


differs from the restraining layer


70


in being comprised of five green sheets


51


, which are stacked and sintered in such a manner that the ceramic sheets


71


and the dummy electrodes


72


are formed. The number of piezo-electric ceramic sheets


40


of the active layer


238


and the number of ceramic sheets


71


of the restraining layer


270


might vary under various conditions.




If the shrinking percentage during calcination of the electrodes provided as the dummy electrodes is within a certain range where the restraining layer


70


is prevented from warping, this layer


70


could be comprised of green sheets


51


only.




With reference to

FIG. 8

, similarly to the modified piezo-electric actuator


203


, the modified piezo-electric actuator


303


includes an active layer


338


including four piezo-electric ceramic sheets


40


. The actuator


303


also includes a restraining layer


370


comprised of five green sheets


50


, each of which has three dummy positive electrodes


73




a


,


73




b


and


73




c


formed on it. The green sheets


50


are stacked and sintered. The dummy electrodes


73




a-




73




c


are grounded through a ground electrode.




If the shrinking percentage during calcination of the dummy positive electrodes is within a certain range where the restraining layer


70


is prevented from warping, this layer


70


could be comprised of green sheets


50


only.




With reference to

FIG. 9

, the modified piezo-electric actuator


403


includes an active layer


438


and a restraining layer


470


similarly to the piezo-electric actuator


3


, but differs from the actuator


3


because the active layer


438


includes four piezo-electric ceramic sheets


40


similarly to the active layers


238


and


338


shown in

FIGS. 7 and 8

, respectively. As shown in

FIG. 4

, the restraining layer


70


of the actuator


3


is comprised of three alternately stacked and sintered green sheets


50


and


51


. The restraining layer


470


of the actuator


403


differs from the restraining layer


70


in being comprised of four stacked green sheets


50


and


51


and another green sheet which forms a ceramic sheet


471


and on which no electrode is formed. This green sheet lies under the green sheets


50


and


51


. The five stacked green sheets are sintered. In other words, even though the ceramic sheet


471


without a dummy electrode forms part of the restraining layer


470


, the vertically symmetric structure of the actuator


403


as a whole causes no warp due to the difference in shrinking percentage during the calcination.




Even though the ceramic sheet


471


differs in thickness from the other ceramic sheets


71


and the piezo-electric ceramic sheets


40


, as shown in

FIG. 9

, the vertically symmetric structure of the actuator


403


as a whole causes no warp due to the difference in shrinking percentage during the calcination.




The operation of the piezo-electric actuator


3


will be described below with reference to

FIGS. 1 and 2

.




If the controller causes the switch


62




a


, for example, to be closed in accordance with certain print data, voltage is applied between the internal negative electrodes


42


and the internal positive electrodes


44




a


, generating electric fields in the piezo-electrically active portions


46




a


of the piezo-electric ceramic sheets


40




a-




40




f


. Consequently, the electrostrictive strain effects of the piezo-electric ceramic sheets develop force with which the active portions


46




a


tend to vertically expand. In the meantime, because no electric field is generated in the ceramic sheets


71




a-




71




c


of the restraining layer


70


, these sheets do not expand nor contract. Therefore, the force with which the active portions


46




a


tend to vertically expand deforms the active layer


38


mainly downward. As indicated with an arrow in

FIG. 2

, the downward deformed active layer


38


reduces the volume of the ink channel


32




a


. This ejects an ink droplet


39


from the ink channel


32




a


through the orifice


37




a


. When the switch


62




a


is opened to cut off the voltage application, the piezo-electrically active portions


46




a


return to the original conditions. This enlarges the ink channel


32




a


, thereby supplying it with ink from the supply device


16


(

FIG. 6

) through a valve (not shown).




Without the restraining layer


70


, the deformation of the piezo-electrically active portions


46




a


would deform the active layer


38


equally upward and downward. The restraining layer


70


, which is highly rigid, and the active layer


38


are sintered into one piece. Even when the switch


62




a


is closed, no electric field is generated in the restraining layer


70


, which does therefore not deform. Consequently, the deformation caused in the active layer


38


mainly deforms the lower side of this layer, which is adjacent to the ink channel


32




a


. Accordingly, the lower side of the piezo-electric actuator


3


can be deformed larger than that of a piezo-electric actuator without a restraining layer


70


, if the piezo-electrically active portions of these actuators deform equally in amount. This makes it possible to reduce the capacity of the ink channel


32




a


and/or eject a larger amount of ink. That is to say, even with the same voltage applied, the provision of the restraining layer


70


makes it possible to eject a larger amount of ink. In other words, it is possible to eject a certain amount of ink by applying a lower voltage. This results in smaller electric power.




The restraining layer


70


of the piezo-electric actuator


3


might be composed of two or more sheets. When the active layer


38


expands into a driven ink channel


32




a


,


32




b


or


32




c


, the driven and adjacent channels decrease or increase in sectional area.

FIG. 3

shows the relationship between the number of sheets of the restraining layer


70


and the change in sectional area of the driven and adjacent channels in the case of the drive voltage being 26 volts. As shown in

FIG. 3

, without the sheet of the restraining layer


70


, the changes in sectional area of the driven and adjacent channels were 3.910×10


−6


mm


2


and 0.900×10


−6


mm


2


, respectively;




with one sheet of the restraining layer


70


, the changes in sectional area of the driven and adjacent channels were 3.588×10


−6


mm


2


and 0.512×10


−6


mm


2


, respectively;




with two sheets of the restraining layer


70


, the changes in sectional area of the driven and adjacent channels were 3.603×10


−6


mm


2


and 0.391×10


−6


mm


2


, respectively;




with three sheets of the restraining layer


70


, the changes in sectional area of the driven and adjacent channels were 3.693×10


−6


mm


2


and 0.394×10


−6


mm


2


, respectively;




with four sheets of the restraining layer


70


, the changes in sectional area of the driven and adjacent channels were 3.784×10


−6


mm


2


and 0.441×10


−6


mm


2


, respectively;




a with five sheets of the restraining layer


70


, the changes in sectional area of the driven and adjacent channels were 3.859×10


−6


mm


2


and 0.496×10


−6


mm


2


, respectively;




with six sheets of the restraining layer


70


, the changes in sectional area of the driven and adjacent channels were 3.916×10


−6


mm


2


and 0.544×10


−6


mm


2


, respectively.




As shown in

FIG. 3

, in the case of no restraining layer


70


being provided, it can be said that the decrease in sectional area of the driven channel


32




a


,


32




b


or


32




c


is large (3.910×10


−6


mm


2


), but the change in sectional area of the adjacent channel/s is large (0.900×10


−6


mm


2


). This large change in sectional area may cause cross talk, which lowers the SN ratio, lowering the printing quality. In this case, the decease in sectional area of the driven channel is large. However, because the rigidity of the active layer


38


is low, a portion of this layer which is positioned over the driven channel deforms laterally as well, spoiling the flatness of the active layer


38


. As a result, a portion or portions of the active layer


38


which are positioned over the adjacent channel/s deform upward, and the wall between the driven channel and the adjacent channel or each of the adjacent channels deforms toward the driven channel, increasing the sectional area of the adjacent channel/s.




In the case of the sheet of the restraining layer


70


being one in number, the portion of the active layer


38


which is positioned over the driven channel


32




a


,


32




b


or


32




c


is restrained from deforming. In this case, the change in sectional area of the driven channel decreases once to 3.588×10


−6


mm


2


, and the change in sectional area of the adjacent channel/s decreases to 0.512×10


−6


mm


2


. Because the rigidity of the piezo-electric actuator


3


is low, however, the deformation of the adjacent channel/s is still large, and therefore the SN ratio is still relatively high.




In the case of the sheets of restraining layer


70


being two in number, their total rigidity is higher, so that the deformation of the upper side of the active layer


38


, which is adjacent to the restraining layer


70


, is smaller, making the piezo-electric actuator


3


more rigid. In this case, the deformation of the adjacent channel/s


32




a


,


32




b


,


32




c


is 0.391×10


−6


mm


2


, which is the smallest. Meanwhile, the deformation of the active layer


38


is efficiently transmitted toward the driven channel


32




a


,


32




b


or


32




c


, so that the change in sectional area of this channel increases to 3.603×10


−6


mm


2


. Because the change in sectional area of the adjacent channel/s is sufficiently small, and the change in sectional area of the driven channel is larger, the SN ratio is improved and therefore the printing quality is improved.




In the case of the sheets of the restraining layer


70


being three or more in number, the deformation of the piezo-electrically active portions


46




a


,


46




b


or


46




c


associated with the driven channel


32




a


,


32




b


or


32




c


is transmitted more efficiently toward this channel, and the change in sectional area of the adjacent channel/s is not large. This maintains a suitable SN ratio.




From the foregoing results, it has been concluded that, for a suitable SN ratio and simple structure of the piezo-electric actuator


3


, the optimum sheet number of restraining layer


70


is three.




Of course, the requirements for the optimum restraining layer


70


vary with the number of sheets and thickness of active layer


38


, the material, the drive voltage, the capacity of the ink channels


32




a-




32




c


, the amount of ejected ink, and other conditions. One of the requirements for the optimum restraining layer


70


is that this layer should make the actuator


3


rigid to such a degree that irregular deformation cannot uselessly deform the ink channel or channels adjacent to a driven ink channel


32




a


,


32




b


or


32




c


. The other requirement is that the restraining layer


70


should be rigid so that the deformation of the piezo-electrically active portions


46




a-




46




c


of the active layer


38


can be transmitted efficiently toward the ink channels


32




a-




32




c.






As stated already, the restraining layer


70


is formed on the top of the active layer


38


integrally with this layer, under which the ink channels


32




a-




32




c


are formed. The restraining layer


70


restrains the deformation of the active layer


38


. This makes it possible to efficiently utilize the deformation of the active layer


38


to change the volume of the ink channels


32




a-




32




c


. It is therefore possible to improve the ink ejecting performance of the print head


15


and reduce power consumption. It is also possible to prevent horizontal or lateral deformation to restrain the volume change of the ink channel or channels adjacent to a driven ink channel


32




a


,


32




b


or


32




c


, preventing cross talk. The active layer


38


and the restraining layer


70


are formed by being integrally sintered. Accordingly, in comparison with a piezo-electric actuator having a deformation restraining member stuck with an adhesive or the like, the actuator


3


can be produced at a low cost by a simple process including a reduced number of steps, and its strength can be high.




The active layer


38


and the restraining layer


70


are made of the same ceramic material. Therefore, green sheets


50


and


51


for the active layer


38


can be used as they are for the restraining layer


70


. This makes it possible to produce the piezo-electric actuator


3


simply at a lower cost. The same material makes the layers


38


and


70


fit together, and prevents them from being warped, distorted or deformed, when they are integrally sintered. This results in high accuracy or precision.




The restraining layer


70


includes dummy electrodes


72


and


73




a-




73




c


and connectors


74


and


75




a-




75




c


, which do not contribute to the deformation for driving the ink channels


32




a-




32




c


. Therefore, when the active layer


38


and the restraining layer


70


are integrally sintered, it is possible to equalize the differences in shrinking percentage in the vertical directions to prevent warps and/or waves due to the difference in shrinking percentage between the layers


38


and


70


. This can made the piezo-electric actuator


3


very flat. Consequently, the actuator


3


can be bonded closely to the cavity layer


30


. This results in high accuracy or precision.




In particular, the internal electrodes


42


and


44




a-




44




c


, connectors


43


and


45




a-




45




c


, dummy electrodes


72


and


73




a-




73




c


and connectors


74


and


75




a-




75




c


are arranged roughly in vertical symmetry in the active layer


38


and restraining layer


70


. Therefore, when these layers


38


and


70


are integrally sintered, it is possible to roughly equalize the differences in shrinking percentage in the vertical directions to prevent warps and/or waves due to the difference in shrinking percentage between the layers


38


and


70


. This can make the piezo-electric actuator


3


even flatter.




The dummy electrodes


72


and


73




a-




73




c


and the connectors


74


and


75




a-




75




c


of the restraining layer


70


face the internal electrodes


42


and


44




a-




44




c


and the connectors


43


and


45




a-




45




c


of the active layer


38


through the ceramics, which are dielectrics, etc. The dummy electrodes and the connectors of the restraining layer


70


are connected electrically to the internal negative electrodes


42


of the active layer


38


. Consequently, there is no potential difference between the dummy electrodes and the connectors of the restraining layer


70


and the internal electrodes and the connectors of the active layer


30


, producing no electric capacity between them. As a result, no electric power is wasted.




The method for producing the piezo-electric actuator


3


in accordance with the present invention involves forming the active layer


38


and the restraining layer


70


by calcining them. The restraining layer


70


restrains the active layer


38


from deforming away from the ink channels


32




a-




32




c


. It is therefore possible to efficiently utilize the deformation of the active layer


38


to change the volume of the ink channels


32




a-




32




c


. This makes it possible to improve the ink ejecting performance of the print head and reduce power consumption. It is also possible to prevent the horizontal or lateral deformation of the active layer


38


to restrain the volume change of the ink channel or channels adjacent to a driven ink channel


32




a


,


32




b


or


32




c


, preventing cross talk. In particular, the active layer


38


and the restraining layer


70


are formed by being integrally sintered. Accordingly, in comparison with the case where a deformation restraining member is stuck with an adhesive or the like, the actuator


3


can be produced at a low cost by a simple process including a reduced number of steps, and its strength can be high.




With reference to

FIG. 10

, similarly to the piezo-electric actuator


3


, the modified piezo-electric actuator


503


consists of an active layer


438


and a restraining layer


570


. The active layer


438


includes six piezo-electric ceramic sheets


40


. The restraining layer


570


includes four ceramic sheets


71


. Each of the two lower ceramic sheets


71


has a dummy negative electrode


72


formed on its upper side. The two upper ceramic sheets


71


have no dummy negative electrode, and can prevent the actuator


503


from deforming due to the provision of the dummy electrodes


72


on the respective lower ceramic sheets


71


. If ceramic sheets having no electrode and large in volume were present adjacently to the internal negative electrodes


42


of the active layer


438


, these negative electrodes


42


would diffuse or spread while the layers


438


and


570


are sintered. Because the dummy negative electrodes


72


are formed on the upper sides of the lower ceramic sheets


71


of the restraining layer


570


, as stated above, the internal negative electrodes


42


can be prevented from diffusing while the layers


438


and


570


are sintered.




The present invention has been described hereinbefore on the basis of the preferred embodiments, but is not limited to them. It would be obvious that various modifications and/or improvements can be made without departing from the spirit of the present invention.



Claims
  • 1. A piezo-electric actuator for an ink jet printer head which has an ink channel with a certain volume and an orifice, and which ejects ink from the channel through the orifice by changing the volume of the channel, the actuator comprising:an active layer one side of which faces the ink channel, the active layer including at least one first sheet formed out of piezo-electric material, the first sheet being provided with an electrode thereon; and a restraining layer which is positioned on the other side of the active layer and restrains the active layer from deforming, the restraining layer including at least one second sheet provided with a dummy electrode.
  • 2. The piezo-electric actuator defined in claim 1, wherein the first and second sheets are formed out of the same material.
  • 3. The piezo-electric actuator defined in claim 1, wherein the dummy electrode of the restraining layer is connected to the electrode of the active layer.
  • 4. The piezo-electric actuator define in claim 1, wherein the dummy electrode of the restraining layer and the electrode of the active layer are positioned in substantial symmetry in the actuator.
  • 5. A piezo-electric actuator for an ink jet printer head, comprising:a laminate including a plurality of piezo-electric sheets stacked and sintered at the same time; and an electrode formed on at least one of the sheets which is positioned on one side of the laminate; only the at least one sheet being activated with a drive voltage, while at least one of the sheets which is positioned on the other side of the laminate is deactivated, wherein said at least one sheet on said other side is provided with a dummy electrode.
  • 6. The piezo-electric actuator defined in claim 5, wherein the print head has an ink channel facing the one side.
  • 7. The piezo-electric actuator defined in claim 5, wherein said at least one sheet on said other side restrains said at least one sheet on the one side from deforming due to the activation thereof.
  • 8. The piezo-electric actuator defined in claim 5, wherein the dummy electrode is connected to the electrode on said at least one sheet on said one side.
  • 9. The piezo-electric actuator defined in claim 5, wherein the dummy electrode is positioned at the at least one sheet on the other side in an equivalent arrangement to the electrode on the at least one sheet on said one side.
  • 10. An ink jet printer head comprising:an ink ejector having an ink channel formed therein and an orifice through which ink is ejected from the channel and a piezo-electric actuator for changing the volume of the ink channel, the actuator including: an active layer one side of which faces the ink channel, the active layer including at least one first sheet formed out of piezo-electric material, the first sheet being provided with an electrode thereon; and a restraining layer which is positioned on the other side of the active layer and restrains the active layer from deforming, the restraining layer including at least one second sheet provided with a dummy electrode.
  • 11. The ink jet printer head defined in claim 10, wherein the first and second sheets are formed out of the same material.
Priority Claims (2)
Number Date Country Kind
11-278828 Sep 1999 JP
2000-258007 Aug 2000 JP
US Referenced Citations (5)
Number Name Date Kind
5402159 Takahashi et al. Mar 1995 A
5639508 Okawa et al. Jun 1997 A
5912526 Okawa et al. Jun 1999 A
20010030490 Wajima et al. Oct 2001 A1
20020051042 Takagi et al. May 2002 A1