Abstract:
A method of directing fluid between a reservoir and a micro-orifice manifold includes the step of providing a piezoelectric actuating element operably associated with independent fluid containment chambers of said manifold. The piezoelectric actuating element is activated by applying a voltage to electrodes which produces fluid flow by changing its geometry inside the reservoir in response to an applied voltage.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     Reference is made to commonly assigned U.S. Pat. No. 5,900,274, issued may 04, 1999, entitled “Controlled Composition and Crystallographic Changes in Forming Functionally Gradient Piezoelectric Transducers” by Chatterjee et al, U.S. patent application Ser. No. 09/071,486 filed May 1, 1998, entitled “Functionally Gradient Piezoelectric Transducers” by Furlani et al, now abandoned, and U.S. Pat. No. 6,013,311, issued Jan. 11, 2000 entitled “Using Morphological Changes to Make Piezoelectric Transducers”, by Chatterjee et al, the disclosures of which are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The invention relates generally to the field of fluid flow and, more particularly, to a method of directing fluid flow through a micro-orifice manifold using a functionally gradient piezoelectric element. 
     BACKGROUND OF THE INVENTION 
     Piezoelectric ink jet elements are used in a wide range of micro-fluidic printing devices. Conventional ink jet elements utilize piezoelectric transducers that comprise one or more uniformly polarized piezoelectric elements with attached surface electrodes. The three most common transducer configurations are multilayer ceramic, mono-morph or bi-morphs, and flex-tensional composite transducers. To activate a transducer, a voltage is applied across its electrodes thereby creating an electric field throughout the piezoelectric elements. This field induces a change in the geometry of the piezoelectric elements resulting in elongation, contraction, shear or combinations thereof. The induced geometric distortion of the elements can be used to implement motion or perform work. In particular, piezoelectric bimorph transducers that produce a bending motion, are commonly used in micro-pumping devices. However, a drawback of the conventional piezoelectric bimorph transducer is that two bonded piezoelectric elements are needed to implement the bending. These bimorph transducers are typically difficult and costly to manufacture for micro-pumping applications (in this application, the word micro means that the dimensions of the element range from  100  microns to  10  mm). Also, when multiple bonded elements are used, stress induced in the elements due to their constrained motion can damage or fracture an element due to abrupt changes in material properties and strain at material interfaces. 
     Therefore, a need persists for an ink jet head that overcomes the aforementioned problems associated with conventional ink jet apparatus. 
     SUMMARY OF THE INVENTION 
     It is, therefore, an object of the present invention to provide a method of directing fluid flow through a micro-orifice manifold actuated by a functionally gradient piezoelectric actuating element. 
     It is a feature of the invention that a functionally gradient piezoelectric transducer is provided integral to the micro-orifice manifold that actuates the flow of fluid between a fluid containment chamber in the manifold and a reservoir. 
     To accomplish these and other objects of the invention, there is provided a method of directing fluid flow between a reservoir and any one of a plurality of independent fluid containment chambers of the micro-fluidic manifold. The method of the invention involves the steps of providing a piezoelectric actuator element (described in details below) in structural relations with each one of the fluid containment chambers. Further included is the step of providing a source of power operably associated with each one of a plurality of first electrodes and a second electrode of the piezoelectric transducer for enabling fluid flow through any one of the plurality of fluid containment chambers of the micro-orifice manifold. The piezoelectric transducer is then actuated in a manner fully described herein for pumping fluid between any one of independent fluid containment chambers of the manifold and the reservoir. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and objects, features and advantages of the present invention will become apparent when taken in conjunction with the following description and drawings wherein identical reference numerals have been used, where possible, to designate identical features that are common to the figures, and wherein: 
     FIG. 1 is a perspective view of the ink jet head of the invention; 
     FIG. 2 is an exploded view of a portion of the ink jet head of the invention; 
     FIG. 3 is a perspective view of a slab of piezoelectric material with a functionally gradient d 31   coefficient; 
     FIG. 4 is a plot of the piezoelectric d 31  coefficient across the width (T) of the slab of piezoelectric material of FIG. 3; 
     FIG. 5 is a plot of piezoelectric d 31  coefficient across the width (T) of a conventional piezoelectric bimorph transducer element, respectively; 
     FIG. 6 is a section view along line  6 — 6  of FIG. 3 illustrating the piezoelectric transducer before activation; 
     FIG. 7 is a section view taken along line  7 — 7  of FIG. 3 illustrating the piezoelectric transducer after activation; 
     FIG. 8 is a section view taken along line  8 — 8  of FIG. 3 illustrating the piezoelectric transducer after activation but under a opposite polarity compared to FIG. 7; 
     FIG. 9 is a perspective view of a single ink jet element of the invention with a partial cut away section illustrating the internal ink storage chamber; 
     FIGS. 10A, l 0 B and  10 C are section views of an ink jet element taken along line  10 — 10  of FIG. 9 showing the ink jet element in an inactivated, drop ejection, and ink refill state, respectively; and, 
     FIGS. 11A,  11 B and  11  are section views of an ink jet element taken along line  11 A— 11 A,  11 B— 11 B,  11 C— 11 C, respectively, of FIG. 9 showing the ink jet element in an inactivated state, drop ejection state, and ink refill state, respectively. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Turning now to the drawings, and particularly to FIGS. 1,  2 , and  9 , a micro-orifice manifold, such as an ink jet head  100 , of the present invention is illustrated. As depicted in FIGS. 1 and 2, the manifold, or alternately ink jet head  100 , comprises a body  110 , a base  120 , and a piezoelectric actuating element  130 . The body  110  has a plurality of separated compartments each having an inlet orifice  140  and outlet orifice  150 . The base  120  and piezoelectric actuating element  130  are fixedly attached to the body  110 . Together, the base  120 , element  130  and body  110  form a contiguous array of independent manifold elements or for instance, ink jet elements  200  (see FIG.  9 ), each of which having fluid containment chamber  220  with an inlet orifice  140  (shown clearly in FIG. 2) and outlet orifice  150  and a piezoelectric actuator  132 . The piezoelectric actuating element  130  comprises a slab  60  of piezoelectric material with first and second opposing surfaces  62  and  64 . A plurality of first surface electrodes  20  are mounted on the first surface  62  and a second surface electrode  22  extends substantially lengthwise along the second surface  64 . Each one of the plurality of first electrodes  20  is operably associated to each one of the plurality of fluid containment chambers  220  (shown clearly in FIG.  9 ). A power source  160  has a plurality of first terminals  156  each one of which being connected to one of the plurality of first surface electrodes  20  via wires  162 . A second terminal  158  is electrically connected to the second surface electrode  22  via wire  164 . The power source  160  can impart a voltage of a specified polarity and magnitude to any one of the plurality of first electrodes  20 , and a different such voltage can be simultaneously applied to any number of the plurality of first electrodes  20 . In addition, the power source  160  can simultaneously apply a different voltage to the second electrode  22  of piezoelectric actuating element  130 . An ink reservoir  170  is connected via fluid conduits  180  to inlet orifices  140  for supplying ink to the ink jet head  100 . The ink jet head  100  is adapted to receive ink from an ink reservoir  170  which is in fluid communications with the inlet orifices  140 , and eject droplets of the ink onto a receiver (not shown) to form an image as will be described. 
     Referring to FIGS. 3,  4  and  5 , a perspective view is shown of the slab of piezoelectric material  60  with a functionally gradient d 31  coefficient. Slab of piezoelectric material  60  has first and second surfaces  62  and  64 , respectively. The width of the slab of piezoelectric material  60  is denoted by T and runs perpendicular to the first and second surfaces  62  and  64 , respectively, as shown. The length of the slab of piezoelectric material  60  is denoted by L and runs parallel to the first and second surfaces  62  and  64 , respectively, as shown. Slab of piezoelectric material  60  is poled perpendicularly to the first and second surfaces  62  and  64  as indicated by polarization vector  70 . 
     Skilled artisans will appreciate that in conventional piezoelectric transducers the piezoelectric “d”-coefficients are constant throughout the slab of piezoelectric material  60 . Moreover, the magnitude of the induced sheer and strain are related to these “d”-coefficients via the constitutive relation as is well known. However, slab of piezoelectric material  60  used in the pumping apparatus  100  of the invention is fabricated in a novel manner so that its piezoelectric properties vary in a prescribed fashion across its width as described below. The d 31  coefficient varies along a first direction perpendicular to the first surface  62  and the second surface  64 , and decreases from the first surface  62  to the second surface  64 , as shown in FIG.  4 . This is in contrast to the uniform or constant spatial dependency of the d 31  coefficient in conventional piezoelectric elements, illustrated in FIG.  5 . 
     In order to form the preferred slab of piezoelectric material  60  having a piezoelectric d 31  coefficient that varies in this fashion, the following method may be used. A piezoelectric block is coated with a first layer of piezoelectric material with a different composition than the block onto a surface of the block. Sequential coatings of one or more layers of piezoelectric material are then formed on the first layer and subsequent layers with different compositions of piezoelectric material. In this way, the piezoelectric element is formed which has a functionally gradient composition which varies along the width of the piezoelectric element, as shown in FIG.  4 . 
     Preferably, the piezoelectric materials used for forming the piezoelectric element is selected from the group consisting of PZT, PLZT, LiNbO3, LiTaO3, KNbO3 or BaTiO3. Most preferred in this group is PZT. For a more detailed description of the method, see cross-referenced commonly assigned U.S. Pat. No. 5,900,274 issued May 04, 1999, to Chattejee et al.; U.S. Ser. No. 09/071,486, filed May 01, 1998, to Furlani et al. (now abandoned); and, U.S. Pat. No. 6,013,311 issued Jan. 11, 2000, to Chatterjee, et al., hereby incorporated herein by reference. 
     Referring now to FIGS. 6-8, the piezoelectric transducer  80  is illustrated comprising slab of piezoelectric material  60  in the inactivated state, a first bending state and a second bending state, respectively. Piezoelectric transducer  80  comprises slab of piezoelectric material  60 , with polarization vector  70 , and first and second surface electrodes  20  and  22  attached to first and second surfaces  62  and  64 , respectively. First and second surface electrodes  62  and  64  are connected to wires  24  and  26 , respectively. Wire  24  is connected to a switch  30  that, in turn, is connected to a first terminal of voltage sour connected to the second terminal of voltage source  40  as shown. 
     According to FIG. 6, the transducer  80  is shown with switch  30  open. Thus there is no voltage across the transducer  80  and it remains unactivated. 
     Referring to FIG. 7, the transducer  80  is shown with switch  30  closed. In this case, the voltage (V) of voltage source  40  is impressed across the transducer  80  with the negative and positive terminals of the voltage source  40  electrically connected to the first and second surface electrodes  20  and  22 , respectively. Thus, the first surface electrode  20  is at a lower voltage than the second surface electrode  22 . This potential difference creates an electric field through the slab of piezoelectric material  60  causing it to contract in length parallel to its first and second surfaces  62  and  64 , respectively and perpendicular to polarization vector  70 . Specifically the change in length (in this case contraction) is given by S(z)=−(d 31 (z) V/T)×L as is well known. Since the functional dependence of the piezoelectric coefficient d 31 (z) increases with z as shown in FIG. 4, the lateral contraction S(z) of the slab of piezoelectric material  60  decreases in magnitude from the first surface  62  to the second surface  64 . Therefore, when the first surface electrode  20  is at a lower voltage than the second surface electrode  22 , the slab of piezoelectric material  60  distorts into a first bending state as shown. It is important to note that the piezoelectric transducer  80  requires only one slab of piezoelectric material  60  as compared to two or more elements for the prior art bimorph transducer (not shown). 
     According to FIG. 8, the transducer  80  is shown with switch  30  closed. In this case, the voltage V of voltage source  40  is impressed across the transducer  80  with positive and negative terminals of the voltage source  40  electrically connected to the first and second surface electrodes  20  and  22 , respectively. Thus, the first surface electrode  20  is at a higher voltage than the second surface electrode  22 . This potential difference creates an electric field through the slab of piezoelectric material  60  causing it to expand in length parallel to its first and second surfaces  62  and  64 , respectively and perpendicular to polarization vector  70 . Specifically, we define S(z) to be the change in length (in this case expansion) in the x (parallel or lateral) direction noting that this expansion varies as a function of z. The thickness of the piezoelectric element is given by T as shown, and therefore S(z)=(d 31 (z) V/T)×L as is well known. The functional dependence of the piezoelectric coefficient d 31 (z) increases with z as shown in FIG.  4 . Thus, the lateral expansion S(z) of the slab of piezoelectric material  60  decreases in magnitude from the first surface  62  to the second surface  64 . Therefore, when the first surface electrode  20  is at a higher potential than the second surface electrode  22 , the slab of piezoelectric material  60  distorts into a second bending state as shown. 
     Referring to FIG. 9 a perspective is shown of one of the contiguous array of ink jet elements  200  of the invention. The ink jet element  200  comprises a body  110 , a base  120 , and a piezoelectric actuator  132 . The base  120  and piezoelectric actuator  132  are fixedly attached to the body  110  as shown, thereby forming an ink storage chamber  220  which is shown in a partial cutaway view. The body  110  comprises an inlet orifice  140  (shown clearly in FIG. 2) and outlet orifice  150 . According to the invention, piezoelectric actuator  132  comprises a slab of piezoelectric material  60  with first and second opposing surfaces  62  and  64 . A first surface electrode  20  is mounted on the first surface  62  of slab  60  and a second surface electrode  22  is mounted on the second surface  64  of slab  60 . A power source  240  has first and second terminals  250 ,  260  that are connected to the first and second surface electrodes  20  and  22 , respectively. An ink reservoir  170  is connected via fluid conduit  180  to inlet orifice  140  for supplying fluid, for example ink, to the fluid containment chamber  220  of the micro-orifice manifold or ink jet element  200 . In application, a receiver  300  may be positioned in front of the outlet orifice  150  for receiving ink drops ejected from the manifold or ink jet element  200  as will be described. 
     Referring now to FIGS. 10A,  10 B, and  10 C, and FIGS. 11A,  11 B, and  11 C section views are shown of ink jet element  200  taken along lines  10 — 10  and  11 — 11  of FIG. 9, respectively. The ink in the ink storage chamber  220  is indicated by the slanted lines  270 . FIGS. 10A and 11A show the ink jet element  200  in an unactivated state. FIGS. 10B and 11B show the ink jet element  200  during ink drop formation and ejection, and FIGS. 10C and 11C show the ink jet element  200  during the ink refill stage. 
     Referring to FIGS. 10A and 11A, when the power source  240  is off, no voltage is applied to the first or second terminals  250  and  260 , and therefore there is no potential difference between the first and second surface electrodes  20  and  22  and the ink jet element  200  is inactive. 
     Referring to FIGS. 10B and 11B, to pump a drop of ink out of the ink storage chamber  220  through the outlet orifice  150 , the power source  240  provides a negative voltage to first terminal  250  and a positive voltage to second terminal  260 . Thus, the first surface electrode  20  is at a lower voltage than the second surface electrode  22 . This creates an electric field through the slab of piezoelectric material  60  causing it to contract in length parallel to the first and second surface electrodes  20  and  22 , as discussed above. Since the functional dependence of the piezoelectric coefficient d 3l (z) increases with (z) as shown in FIG. 4, the lateral contraction of the slab of piezoelectric material  60  decreases in magnitude from the first surface electrode  20  to the second surface electrode  22 , thereby causing the slab of piezoelectric material  60  to deform into a first bending state as shown in FIG.  7 . This, in turn, decreases the free volume of the ink storage chamber  220  thereby increasing the pressure to such a level that a drop of ink  290  is ejected out through outlet orifice  150  and ultimately onto a receiver  300 . 
     Referring to FIGS. 10C and 11C, to draw ink into the ink storage chamber  220  from the ink reservoir  170 , the power source  240  provides a positive voltage to terminal  250  and a negative voltage to terminal  260 . Thus, the first surface electrode  20  is at a higher voltage than the second surface electrode  22 . This potential difference creates an electric field through the slab of piezoelectric material  60  causing it to expand in length parallel to the first and second surface electrodes  20  and  22  as discussed above. Since the functional dependence of the piezoelectric coefficient d 31  (z) increases with (z) as shown in FIG. 4, the lateral expansion of the slab of piezoelectric material  60  decreases in magnitude from the first surface electrode  20  to the second surface electrode  22 , thereby causing the slab of piezoelectric material  60  to deform into a second bending state as shown in FIG.  8 . This, in turn, increases the free volume of the ink storage chamber  220  thereby decreasing the pressure in the ink storage chamber  120  so that it is less than in the reservoir  170 . Under this condition ink flows form the reservoir  170  via the conduit  180 , through the inlet orifice  140  into the ink storage chamber  220 . 
     The operation of the ink jet head  100  can now be understood via reference to FIGS. 1,  2 ,  9 ,  10 , and  11 . To eject a drop of ink out of one of the plurality of ink storage chambers  220 , the power source  160  simultaneously imparts a voltage to the first surface electrode  20  that is operably associated with the respective ink storage chamber  220 , and a different voltage to the second surface electrode  22  such that the respective first surface electrode  20  is at a lower voltage than the second surface electrode  22 . This creates an electric field through a portion of the slab of piezoelectric material  60  between the respective first surface electrode  20  and the second surface electrode  22  thereby causing it to contract in length parallel to the respective first surface electrode  20  and second surface electrode  22 , as discussed above. Since the functional dependence of the piezoelectric coefficient d 3l  (z) increases with (z) as shown in FIG. 4, the lateral contraction of the portion of the slab of piezoelectric material  60  between the respective first surface electrode  20  and the second surface electrode  22  decreases in magnitude from the respective first surface electrode  20  to the second electrode  22 , thereby causing the portion of the slab of piezoelectric material  60  between the respective first surface electrode  20  and the second surface electrode  22  to deform into a first bending state as shown in FIG.  7 . This, in turn, decreases the free volume of the respective ink storage chamber  220  thereby increasing the pressure of the ink in the respective ink storage chamber  220  to such a level that a drop of ink  290  is ejected out through outlet orifice  150  of the respective ink storage chamber  220  and ultimately onto a receiver  300 . 
     To draw ink into one of the plurality of the ink storage chambers  220  of the ink jet head  100  from the ink reservoir  170 , the power source  160  simultaneously imparts a voltage to the of first surface electrode  20  that is operably associated with the specified ink storage chamber  220  and a different voltage to the second surface electrod  22  such that the respective first surface electrode  20  is at a higher voltage than the second surface electrode  22 . This creates an electric field through a portion of the slab  60  between the respective first surface electrode  20  and the second surface electrode  22  thereby causing slab  60  to expand in length parallel to the respective first surface electrode  20  and second surface electrode  22 , as discussed above. Since the functional dependence of the piezoelectric coefficient d 31  (z) increases with (z) as shown in FIG. 4, the lateral expansion of the portion of the slab of piezoelectric material  60  between the respective first surface electrode  20  and the second surface electrode  22  increases in magnitude from the respective first surface electrode  20  to the second surface electrode  22 , thereby causing the portion of the slab of piezoelectric material  60  between the respective first surface electrode  20  and the second surface electrode  22  to deform into a second bending state as shown in FIG.  7 . This, in turn, increases the free volume of the respective ink storage chamber  220  thereby decreasing the pressure in the respective ink storage chamber  220  so that it is less than in the ink reservoir  170 . Under this condition ink flows from the ink reservoir  170  via the conduit  180 , through the inlet orifice  140  into the respective ink storage chamber  220 . 
     Therefore, the invention has been described with reference to a preferred embodiment. However, it will be appreciated that variations and modifications can be effected by a person of ordinary skill in the art without departing from the spirit and scope of the invention. 
     
       
         
               
             
               
               
               
             
           
               
                   
               
             
             
               
                 PARTS LIST 
               
             
          
           
               
                   
                 20 
                 first surface electrode 
               
               
                   
                 22 
                 second surface electrode 
               
               
                   
                 24 
                 wire 
               
               
                   
                 26 
                 wire 
               
               
                   
                 30 
                 switch 
               
               
                   
                 40 
                 voltage source 
               
               
                   
                 60 
                 slab of piezoelectric material 
               
               
                   
                 62 
                 first surface 
               
               
                   
                 64 
                 second surface 
               
               
                   
                 70 
                 polarization vector 
               
               
                   
                 80 
                 piezoelectric transducer 
               
               
                   
                 100 
                 piezoelectric ink jet head 
               
               
                   
                 110 
                 body 
               
               
                   
                 120 
                 base 
               
               
                   
                 130 
                 piezoelectric actuating element 
               
               
                   
                 132 
                 piezoelectric actuator 
               
               
                   
                 140 
                 inlet orifice 
               
               
                   
                 150 
                 outlet orifice 
               
               
                   
                 156 
                 first terminal 
               
               
                   
                 158 
                 second terminal 
               
               
                   
                 160 
                 power source 
               
               
                   
                 162 
                 wires 
               
               
                   
                 164 
                 wire 
               
               
                   
                 170 
                 reservoir 
               
               
                   
                 180 
                 conduit 
               
               
                   
                 200 
                 ink jet element 
               
               
                   
                 220 
                 ink storage chamber 
               
               
                   
                 240 
                 power source 
               
               
                   
                 250 
                 first terminal 
               
               
                   
                 260 
                 second terminal