Abstract:
A device for sensing pressure using two flexible diaphragms in which an additional element is added to promote rolling contact of the diaphragm. One embodiment aligns the flexible diaphragms in a non-parallel alignment such that deflection of one flexible diaphragm will roll with respect to the other to provide increased linear capacitive response. In another embodiment a non-conductive spacing element is positioned between the diaphragms to permit rolling contact upon displacement of a diaphragms. These devices are capacitive pressure gauges. One additional embodiment includes a cantilever hinge and rigid polymer disc to convert one diaphragm into a linearly deflecting diaphragm.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates in general to pressure sensor technology and, more particularly, to low cost pressure sensors for either disposable or high volume applications of pressure sensors for gas and liquid based pressure sensing with increased sensitivity, improved linearity, and even lower cost. This is a continuation-in-part of a prior application filed on Dec. 30, 2003, having Ser. No. 10/748,817, which is incorporated herein by reference in its entirety.  
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     Modern industrial, commercial, aerospace and military systems depend critically on reliable pumps for fluid handling. Both gas and liquid fluids take advantage of smaller, more distributed and more portable systems for increasing uses in instrumentation and control. An improved electrostatic pump has been developed, as described in U.S. Pat. No. 6,179,586. In this patent, the pump consists of a single molded plastic chamber with two thin diaphragms stacked directly on top of each other. The diaphragms are actuated, depending on design, with electrostatic, electromagnetic or piezoelectric methods. This patent describes the use of a single chamber for pumping.  
         [0003]     Out of this technology has come a need for improved pressure sensors that can use the speed and efficiency of the multiple diaphragm operation from a single molded plastic chamber. However, to make a pressure sensor operate optimally, the response to pressure changes should be as linear as possible.  
         [0004]     It would be of great advantage if a pressure sensors using mesopump construction would have improved sensitivity.  
         [0005]     Another advantage would be if a pressure sensors using mesopump construction would have increased linearization.  
         [0006]     Yet another advantage would be if mesopump technology could be modified to be produced at less cost for use both as sensors and valves.  
         [0007]     Other advantages and features will appear hereinafter.  
       SUMMARY OF THE INVENTION  
       [0008]     The present invention provides improvements in low cost, effective meso-pressure sensors that are capable of measuring both positive and negative pressure, depending upon how the device is configured. It is made from inexpensive, injection molded plastics and plastic films that are readily available from many commercial sources.  
         [0009]     The sensors include a sealed chamber defining part, a first flexible diaphragm mounted on one side in communication with the sealed chamber and a second flexible diaphragm separated from the first diaphragm by an insulator. A sensor chamber defining part is mounted on the other side of the second diaphragm for communication with a sensing atmosphere.  
         [0010]     In an embodiment of the present invention, the first and second flexible diaphragms are mounted in a non-parallel alignment with each other, deflection of one flexible diaphragm will roll with respect to the other to provide increased linear capacitive response. In an alternative embodiment, a non-conductive spacer element is positioned between the diaphragms to separate them while permitting rolling contact upon displacement of at least one of the diaphragms. In both embodiments, the spacer, whether in the middle or at the periphery, causes the contact between the diaphragms to roll with respect to each other to provide a linear response. In another embodiment, a cantilever hinge and tab of a rigid polymer disc is mounted in the chamber between the first flexible diaphragm and the chamber to thereby convert the first flexible diaphragm into a linearly deflecting diaphragm.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     For a more complete understanding of the invention, reference is hereby made to the drawings, in which: invention as non-parallel diaphragms sensor;  
         [0012]      FIG. 2  is an exploded plan view of the embodiment shown in  FIG. 1 ;  
         [0013]      FIG. 3  is a side elevational view, in section, of another embodiment of the present invention as a dual diaphragm sensor; and  
         [0014]      FIG. 4  is bottom view of the embodiment shown in  FIG. 3 ;  
         [0015]      FIG. 5  is a side elevational view, in section, of one embodiment of the present invention as a cantilever style sensor;  
         [0016]      FIG. 6  is an exploded plan view of the embodiment shown in  FIG. 5 . 
     
    
       [0017]     In the figures, like reference characters designate identical or corresponding components and units throughout the several views.  
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0018]     All of the pressure sensors of this invention have elements disclosed in a prior, commonly owned application by the same inventors and filed on Dec. 30, 2003, having Ser. No. 10/748,817, which has been incorporated herein above by reference in its entirety. The sensor includes a sealed chamber defining part and a first flexible diaphragm having two sides and mounted on one side in communication with the chamber in the sealed chamber defining part. A first flexible diaphragm has a conductive surface and an insulator is mounted on the other side of the first flexible diaphragm. A second flexible diaphragm having two sides is mounted on one side in communication with the insulator. The second flexible diaphragm also has a conductive surface and is in communication with a sensor chamber defining part mounted on the other side of the second flexible diaphragm, which chamber has an opening for communication with a sensing atmosphere. Measurement of the capacitance between the diaphragms is a function of the pressure in the sensor chamber introduced through the opening and causing the one flexible diaphragms to move with respect to the other of the flexible diaphragms.  
         [0019]     Referring to the figures,  FIG. 1  illustrates a pressure sensor  10  generally that has an upper chamber forming element  11  defining closed chamber  13  and a lower chamber forming element  15 , to define an open chamber  17 , having port  19 . The chamber defining elements  11  and  17  may be made from plastic or other nonconductive materials and may be molded or fabricated. Neither part  11  or  17  has any metallization or other patterning. An upper diaphragm  21  is mounted on the closed chamber forming element  13  and is spaced at an angle with respect to a vertical axis  23  by spacer  25 .  
         [0020]     Diaphragm  21  may be a plastic film with metallization or a dielectric film. Diaphragm  21  may be perforated and remains rigid curing operation. A lower diaphragm  27  is mounted on the lower chamber forming element  15  and on the other side of spacer  25 . Diaphragm  27  may be a plastic film, either with metallization or formed from dielectric film and forms sealed cavity or closed chamber  13 . Spacer  25  is also preferably made from plastic and contains no metallization. Spacer  25  separates diaphragms  21  and  27  at an angle with respect to axis  25 .  
         [0021]     Since diaphragm  27  is flexible, pressure in open chamber  17  will cause it to have increased contact with diaphragm  21 , thus providing a linear pressure sensor.  
         [0022]      FIG. 2  is an exploded view of the parts of  FIG. 1 , shown in plan view. Upper chamber forming element  11  includes a cavity or backstop  31  and holes  33  which are open for electrical contact elements  36 . Diaphragm  21  includes hole  33  for electrical contact, and may have holes  35  and does include a contact point  37 . Spacer  25 , which is pie shaped as shown in section in  FIG. 1  and in plan view in  FIG. 2 , also has a hole  33  for electrical contact. Diaphragm  27  is not perforated and has contact point  37  for contact with elements  36 . Finally, lower chamber defining element  15  provides pressure access via port  19  and includes cavity  39 . In an optional embodiment, chamber  15  may be replaced by a ring or other mounting means for mounting diaphragm  27  to spacer  25 .  
         [0023]     As can be appreciated, the device of  FIGS. 1 and 2  provides for linear diaphragm deflection by initially setting one diaphragm at an angle to the other. When the deforming diaphragm deflects, it will roll along the other diaphragm, creating a more linear capacitive response than prior designs.  
         [0024]     In  FIG. 3 , additional elements of the present invention are shown. Instead of spacer  25  of  FIG. 1 , a spacer element  45  is mounted between diaphragms  21  and  27  which are mounted on their respective peripheral edges by mounting elements  47  and include electrical contacts  49 . Upper chamber element  11  and lower chamber element  15  are not shown in this view for simplicity of explanation. Spacer  45  is a nonconductive element of any shape, such as spherical or cubical, and may be a patterned SU8 pillar. Spacer  45  is molded or otherwise formed. Operation is the same as in  FIG. 1 , however, as pressure from pressure source  51  causes lower diaphragm  27  to deflect, once again causing a more linear capacitive response than prior designs. Spacer  45  initially keeps diaphragms  21  and  27  separated and allows rolling capacitive contact as the films  21  and  27  come into contact. Rolling contact actuation provides very high capacitive change relative to displacement and very high force for electro-static actuation. Diaphragm  21  in any embodiment has holes  33  to allow readout  53  if desired.  
         [0025]     When both diaphragms  21  and  27  are sealed and do not have any holes  35 , such as when chamber elements  1  and  15  permit communication only via port  19  to a sealed system, the device of this invention serves as an absolute pressure sensor. In the second embodiment shown in  FIGS. 3 and 4 , pressure can be sensed on both sides of the device and may have increased sensitivity when compared to a device with only one deflecting diaphragm, such as in  FIGS. 1 and 2 . The device shown in  FIGS. 3 and 4  also has the capability of differential sensing because diaphragms  21  and  27  will move asymmetrically if the pressures from the two sides are different.  
         [0026]     Turning now to  FIGS. 5 and 6 , a similar embodiment is shown with an upper chamber forming element  11  defining closed chamber  13  and a lower chamber forming element  15 , to define an open chamber  17 , having port  19 . An upper diaphragm  21  is mounted on the closed chamber forming element  13  and lower diaphragm  27  is mounted on the lower chamber forming element  15 . Spacer  55  separates diaphragms  21  and  27  as in the patent application from which this application depends. Spacer  55  is also preferably made from plastic and contains no metallization. Also included in this embodiment is cantilever  57 , which supports a rigid part  59  such that cantilever  57  and rigid part  59  are located behind the deflecting diaphragm  27 . Rigid element  59  converts the normal ballooning movement of a conventional deflecting diaphragm  27  into a linearly deflecting behavior.  
         [0027]     The sensing atmosphere may be any fluid, including gases such as the atmosphere, gas pumps, chemical and electrolytic reactions, and the like or including liquids such as reactors, test devices, pumps and the like.  
         [0028]     While particular embodiments of the present invention have been illustrated and described, they are merely exemplary and a person skilled in the art may make variations and modifications to the embodiments described herein without departing from the spirit and scope of the present invention. All such equivalent variations and modifications are intended to be included within the scope of this invention, and it is not intended to limit the invention, except as defined by the following claims.