Abstract:
A valve comprises an orifice plate ( 1 ) having one or more orifices ( 4 ) through which a fluid may flow, and one or more piezo-electric elements ( 2 ). Each element ( 2 ) has a face positioned to contact the orifice plate at an orifice. Each element has a first state in which it abuts the plate to prevent flow of fluid through the associated orifice and a second state in which the face is spaced from the plate to allow flow through the associated orifice. A controller ( 50 ) selectively applies a first voltage to an elements to cause it to adopt the first state and applies a second voltage to the one or more elements to cause the elements to adopt the second state.

Description:
BACKGROUND 
     Some applications of valves require a valve which is small and operable at high frequency. One example, amongst others, of such an application is an air valve array for a fluid dispenser for example an ink jet printer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various features and advantages of the present disclosure will be apparent from the detailed description which follows, taken in conjunction with the accompanying drawings, which together illustrate, by way of example only, features of the present disclosure, and wherein: 
         FIG. 1A  is a schematic diagram of an example of a valve: 
         FIG. 1B  is a schematic end view of an orifice plate of the valve of  FIG. 1A ; 
         FIG. 2A  is a schematic cross sectional view of the valve of  FIG. 1  with the valve closed and  FIG. 2B  is a partial view showing the valve open; 
         FIG. 3A  is a schematic view of a fluid dispenser including the valve of  FIG. 2  open and  FIG. 3B  shows the fluid dispenser with the valve closed; 
         FIGS. 4A and 4B  are schematic diagrams showing relative positions of the orifice plate and fluid drops; 
         FIG. 5  is a graph showing the relationship of droplet deflection and relative position of the orifice plate and fluid drops; 
         FIG. 6  is a graph showing the variation of the width of an air jet with distance from the orifice plate: 
         FIG. 7  is a schematic diagram showing jets produced by the orifice plate; 
         FIG. 8  is a graph showing he variation of droplet displacement with distance from the orifice plate: and 
         FIG. 9  is a schematic diagram of a fluid dispensing apparatus. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1A , the valve comprises an orifice plate  1  and a plurality of elongate piezo-electric elements  2  supported by a support  6 . The orifice plate I defines a plurality of orifices  4 , one for each piezo-electric element  2 , through which a fluid may flow. In examples described below the fluid is gas. Each piezoelectric element  2  has electrodes (not shown) arranged in known manner relative to the polarity of the element to cause the length of the element  2  to change linearly in a direction perpendicular to the orifice plate  1  when a voltage is applied to the electrodes. In one state, an element  2  abuts the orifice plate  1  and blocks the orifice (indicated by  4 A for example) associated with it and in another state the element is spaced from the orifice plate  1  and thus the associated orifice (indicated by  4 B for example) is not blocked. 
     As will be described hereinbelow, such a valve may have very small dimensions; for example there may be ten to twenty or more piezoelectric elements per mm. The valve can operate at high frequency; some examples operate at 250 kHz. A piezo-electric element of PMN-PT (Lead Magnesium Niobate-Lead Titanate) may change in length by 4 micrometers in 4 microseconds with an applied voltage of 60V. Whilst the example of  FIG. 1  has a plurality of piezoelectric elements and orifices, it will be appreciated that a valve could have only one element and one orifice. Furthermore, whilst the example of  FIG. 1  shows for simplicity only seven piezo-electric elements  2  and orifices  1 , the valve may have any other number of elements and orifices. For example the valve may have hundreds of elements and orifices. Examples of the valves may have 10 to 20 orifices per mm. The orifices may have a diameter of 10 to 50 micrometers. In an example the orifices have a diameter of 40 micrometers. The width W of each piezoelectric element may be 40 to 80 micrometers. 
     Referring to  FIGS. 2A and 2B , an example of the valve comprises a closed chamber  10  defined by a support  6 , the orifice plate  1 , a hood  8 , an end wall  16  opposite the orifice plate, and lateral end walls (not shown) which extend between the orifice plate and the end wall. The orifice plate  1 , hood  8  and support  6  may be of any suitable stiff material for example silicon, stainless steel, beryllium copper, or other metals. In an example of the valve, the orifice plate is of silicon. The support  6  supports at least one, in this example a plurality of, piezo-electric elements  2  within the chamber  10 . Each element  2  is fixed to the support at one end remote from the orifice plate  1 , the remainder of the element being free to move, sliding on the support  6 , to block and unblock an orifice in the plate  1 . In the example of  FIGS. 2A and 2B , the piezo-electric element is fixed to the support by adhesive. The chamber has an inlet port  14  in this example for supplying pressurized gas, in this example air, from a source (not shown) to the chamber  10 . An actuating voltage is applied to each element  2  by an actuator  50  coupled to the electrodes of the piezo-electric element  2  by conductors  54 . In a first state of the actuating voltage the piezo-electric element  2  abuts the orifice plate  1  and blocks its associated orifice as shown in  FIG. 2A . In a second state of the actuating voltage the piezo-electric element  2  is spaced from the orifice plate  1  and the pressurized air exits the chamber through the orifice as an air jet as shown in  FIG. 2B . 
     The actuator  50  may be responsive to control signals  52  from a control device for example a computer which controls the operation of the valve. 
     Referring to  FIGS. 3A and 3B , the valve may be used in a fluid ejection system which in this example is an ink jet printer.  FIGS. 3A and 3B  schematically show, for simplicity, one section, associated with one piezo-electric element  2  and one orifice  4 , of a print head  40 . The print head comprises one or more valves. 
     The section of the print head  40  shown in  FIGS. 3A and 3B  comprises a source  56  of ink which supplies ink under pressure to a nozzle  60 . The source  56  and nozzle  60  are vibrated by a vibrator  58  which may be a piezo-electric vibrator to create ink drops  62  which are jetted towards a print medium  36 . The ink drops are jetted along a drop path past the valve before they reach the print medium  36 . When the orifice  4  is not blocked as shown in  FIG. 3A , an air jet  48  diverts one or more drops into a gutter  66  for recirculation back to an ink reservoir ( 38  in  FIG. 9 ) via a suction tube  68 . When the orifice is blocked as shown in  FIG. 3B , the drops are not diverted and reach the print medium. The print medium and the print head move one relative to the other and drops are allowed to reach the print medium or be diverted to the gutter under the control of a data source to print desired indicia on the medium  36  as will be described with reference to  FIG. 9 . 
     Referring to  FIGS. 4A and 4B , an example of the print head  40  (see  FIG. 3A ) has a plurality of nozzles  60  and a like plurality of orifices  4  and piezoelectric elements  2 . In an example, each nozzle is arranged to produce drops of fluid having a volume of about 14 picolitres at a rate of 135 KHz. The orifices in the orifice plate have a diameter of about 18 micrometers and are spaced by 338/2=169 micrometers. Air is supplied to the chamber  10  (see  FIG. 3A ) at a pressure of about 0.45 bar producing air jets when the orifices  4  are open of about 1.5 bar.  FIG. 4A  shows the air jets  48  aligned with the drops and  FIG. 4B  shows the air jets  48  offset in the X direction, the direction of the path of the drops, from the drops by 338 micrometers. The orifice plate is spaced from the drop path by the spacing Y. 
       FIG. 5  is an example graph showing the variation in angle of drop deflection with direction X for two values of Y, 0.2 mm and 0.4 mm.  FIG. 7  is an example graph showing the width of an air jet with distance from the orifice plate.  FIG. 6  shows, consistently with  FIG. 5 , a working range of value Y of 0.1 mm to 0.2 mm.  FIG. 7  shows that at 0.2 mm form the orifice plate the air jets  48  do not overlap minimizing cross talk between adjacent orifices.  FIG. 8  is an example graph showing the variation with orifice to drop distance Y of drop deflection at 1 mm from the drop plate, it shows that over the working range of Y=0.1 to 0.2 mm the deflection vanes approximately linearly. 
     In one example, the number of orifices and of piezoelectric elements in a valve is selectable by the designer. An array of a plurality of valves each comprising one or more orifices and piezoelectric elements may be used in one print head. 
     The dimensions and spacing of the orifices and of the piezo-electric elements is selectable by the designer. In practice, the dimensions and spacing may be limited by the chosen method of making the piezoelectric elements. In one example the elements are made by mechanically cutting a piezo-electric crystal which provides a minimum spacing between adjacent elements of about 10 micrometers. Referring to  FIGS. 1 and 2 , illustrative dimensions for a piezo-electric element are 5 mm long (L perpendicular to the orifice plate  1 ), 0.1 mm thick (D) and 0.08 mm wide (W parallel to the orifice plate) for an orifice  4  of diameter less than 0.08 mm. Such dimensions are suitable for printing at a resolution of about 250 dots per inch (dpi) using 10 piezoelectric elements and orifices per mm. With other methods of making the elements, smaller dimensions may be achieved. 
       FIG. 9  schematically shows an example of an inkjet printing system  20  using the valve described herein above. The inkjet printing system  20  constitutes one example of a fluid ejection system that includes a fluid ejection device, such as inkjet print head assembly  22 , and a fluid supply assembly, such as ink supply assembly  24 . The inkjet printing system  20  also includes a mounting assembly  26 , a media transport assembly  28 , and an electronic controller  30 . At least one power supply  32  provides power to the various electrical components of inkjet printing system  20 . 
     In one example, inkjet print head assembly  22  includes one or more print heads  40  as described above that eject drops of ink through a plurality of nozzles  60  toward a print medium  36  so as to print onto print medium  36 . 
     Print medium  36  may be any type of suitable sheet material, such as paper, card stock, transparencies, Mylar, fabric, and the like. 
     Typically, nozzles  60  are arranged in one or more columns or arrays such that properly sequenced ejection of ink from nozzles  60  causes characters, symbols, and/or other graphics or images to be printed upon print medium  36  as inkjet print head assembly  22  and print medium  36  are moved relative to each other. While the following description refers to the ejection of ink from print head assembly  22 , it is understood that other liquids, fluids or flowable materials, including dear fluid, may be ejected from print head assembly  22 . 
     Ink supply assembly  24  as one example of a fluid supply assembly  30  provides ink to print head assembly  22  and includes a reservoir  38  for storing ink. As such, ink flows from reservoir  38  to inkjet print head assembly  22 . Ink supply assembly  24  arid inkjet print head assembly  22  form a recirculating ink delivery system as described above. In a recirculating ink delivery system as shown in  FIGS. 3A and 3B , only a portion of the ink provided to print head assembly  22  is consumed during printing. Ink not consumed during printing is returned to ink supply assembly  24 . 
     In one example, inkjet print head assembly  22  and ink supply assembly  24  are housed together in an inkjet cartridge or pen. The inkjet cartridge or pen is one example of a fluid ejection device. In another example, ink supply assembly  24  is separate from inkjet print head assembly  22  and provides ink to inkjet print head assembly  22  through an interface connection, such as a supply tube (not shown), In either example, reservoir  38  of ink supply assembly  24  may be removed, replaced, and/or refilled. In one example, where inkjet print head assembly  22  and ink supply assembly  24   15  are housed together in an inkjet cartridge, reservoir  38  includes a local reservoir located within the cartridge and may also include a larger reservoir located separately from the cartridge. As such, the separate, larger reservoir serves to refill the local reservoir, for example source  56  of  FIG. 3 . Accordingly, the separate, larger reservoir and/or the local reservoir may be removed, replaced, and/or refilled. 
     Mounting assembly  26  positions inkjet print head assembly  22  relative to media transport assembly  28  and media transport assembly  28  positions print medium  36  relative to inkjet print head assembly  22 . Thus, a print zone  37  is defined adjacent to nozzles  60  in an area between inkjet print head assembly  22  and print medium  36 . 
     In one example, inkjet print head assembly  22  is a scanning type print head assembly. As such, mounting assembly  26  includes a carriage not shown) for moving inkjet print head assembly  22  relative to media transport assembly  28  to scan print medium  36 . The assembly  26  comprises for example a print head  40  having a plurality of orifices  4  and piezoelectric elements  2  extending in the direction of movement of the print medium. The carriage scans the print head  40  across the print medium to simultaneously print a plurality of lines across the medium. 
     In another example, inkjet print head assembly  22  is a non-scanning type print head assembly As such, mounting assembly  26  fixes inkjet print head assembly  22  at a prescribed position relative to media transport assembly  28 . Thus, media transport assembly  28  positions print medium  36  relative to inkjet print head assembly  22 . The assembly comprises a fixed array of print heads extending perpendicular to the direction of movement of the print medium. Each print head comprises a plurality of drop sources, orifices  4  and piezo-electric elements  2  arranged to simultaneously print on the print medium  36 . 
     Electronic controller or printer controller  30  typically includes a processor, firmware, and other electronics, or any combination thereof, for communicating with and controlling inkjet print head assembly  22 , mounting assembly  26 , and media transport assembly  28 . Electronic controller  30  receives data  39  from a host system, such as a computer, and usually includes memory for temporarily storing data  39 . Typically, data  39  is sent to inkjet printing system  20  along an electronic, infrared, optical, or other information transfer path. Data  39  represents, for example, a document and/or file to be printed. As such, data  39  forms a print job for inkjet printing system  20  and includes one or more print job  10  commands and/or command parameters. 
     In one example, the controller  30  sends control data  52  to the actuating device  50  shown in  FIG. 2A  to actuate the valve and to control which drops  62  reach the print medium  36 . As such, electronic controller  30  defines a pattern of ejected ink drops that form characters, symbols, and/or other graphics or images on print medium  36 . The pattern of  15  ejected ink drops is determined by the print job commands and/or command parameters. 
     The piezo-electric elements of the examples described above are of PMN-PT but other examples could use other piezo-electric materials for example PZT (Lead Zirconium Titanate). PMN-PT allows higher frequency operation and allows smaller dimensions to be achieved than other materials currently available. The piezo electric elements described above have a rectangular cross section, but could have other cross-sectional shapes. The piezoelectric elements described above change length linearly to block and unblock the orifices  4 . In other examples, the elements may bend to block and unblock the orifices but such a mode of operation is slower that changing length linearly. 
     The valve of  FIGS. 1 and 2  may be used for purposes other than in a fluid ejection system as described with reference to  FIGS. 3 to 9 .