A DEVICE FOR SENSING FLUID PRESSURE
FIELD OF INVENTION
[001] The embodiments herein generally relate to a device for sensing fluid pressure. More specifically  it relates to a device capable of sensing fluid pressure wherein said device works on the principle of differential expansion for sensing and measuring pressure of a fluid under consideration  wherein the differential expansion is a result of asymmetry of the tube or bellow  made of metallic or composite material  on application of fluid pressure. A method of measuring the fluid pressure using the same is also provided.
BACKGROUND OF THE INVENTION
[002] Pressure sensing devices are indispensable instruments in today’s machine driven age. At present numerous pressure sensing devices are being commonly employed in diverse environments for a variety of applications including commercial and industrial.
[003] A typical mechanical pressure sensing device comprises a sensing element that deflects in response to applied pressure of the fluid  whose pressure is to be measured  a pointer attached suitably to the deflecting portion of the sensing element  which moves in front of a calibrated scale to provide a value of the fluid pressure being measured. These types of pressure sensing devices are categorized under mechanical pressure sensors as they involve a mechanical sensing element for sensing the pressure. The measured value may be displayed in a form such as analog  digital or hybrid.
[004] The sensing element of the pressure sensing device typically comprises Bourdon tubes  diaphragms  capsules  bellows etc.  wherein well calibrated displacement or deflection of the sensing element from the original position is used to measure the pressure of the fluid under consideration.
[005] For example  in a Bourdon tube  a flattened tube  which forms the sensing element herein  is a C shape tube with oval cross-section. The flattened tube when pressurized tends to change to be straightened or uncoil  elastically. The material of make of the Bourdon tube may be metals like Stainless Steel  Phosphor Bronze and Beryllium Copper etc.
[006] In some other pressure sensing devices  a diaphragm is used as a sensing element  wherein the diaphragm expands or contracts in response to the increase or decrease of the fluid pressure  which may be measured using a pointer that is displaced against a dial of calibrated pressure values.
[007] The pressure sensing devices described hereinabove are  accurate and simple in construction. However  they respond slowly to changes in the pressure and are subjected to hysteresis.
[008] Further  it is an observation that the manufacturing process of the flattened or oval C shaped Bourdon tube is cumbersome owning to dual process of flattening and bending.
[009] Additionally  the manufacturing cost of the C shaped oval Bourdon tube is more because of the shape or the geometry of the tube.
[0010] It is further observed that the Bourdon tube pressure gauge is difficult to miniaturized to a level of micro or Nano scale  because all the mechanical elements (gear  gear sector  links etc) are to be placed at center of curvature of the C-shaped flattened tube. Mechanical elements  like pinion gears and gear sector  are still required in the above said pressure gauges to measure the pressure either analog or digital way or in a hybrid manner.
[0011] It is also desired to have a pressure sensing device which can be used to measure the vacuum pressure.
[0012] Therefore  there is a need in the art for providing a pressure sensing device which is not only low cost  accurate  painless to miniaturize  and simple in construction  but also can respond fast to changes in pressure  can measure vacuum pressure and is less prone to hysteresis. Further  there is a need to have a pressure sensing device which has a shape or geometry which is convenient to manufacture and do not need mechanical elements to digitize.
OBJECTS OF THE INVENTION
[0013] A main object of the present invention is to provide a pressure sensing device.
[0014] Another object of the present invention is to develop a pressure sensing device and a method of measuring pressure of the fluid using the pressure sensing device.
[0015] Still another object of the present invention is to provide a low cost pressure sensing device.
[0016] Yet another object of the present invention is to provide a pressure sensing device that is accurate  small and simple in construction.
[0017] Another object of the present invention is to provide a pressure sensing device that can be digitized without any mechanical elements.
[0018] Another object of the present invention is to provide a pressure sensing device that has a geometry or shape which is convenient to manufacture.
[0019] Another object of the present invention is to provide a pressure sensing device that has a geometry or shape which is suitable to manufacture at low cost.
[0020] Another object of the present invention is to provide a pressure sensing device that has a geometry or shape which is suitable to miniaturize.
[0021] Another object of the present invention is to provide a pressure sensing device that can measure vacuum pressure.
[0022] Another object of the present invention is to provide a pressure sensing device that responds quickly to changes in the pressure.
[0023] Another object of the present invention is to provide a pressure sensing device that is less prone to hysteresis.
[0024] The other objects and advantages of the present invention will be apparent from the following description when read in conjunction with the accompanying drawings which are incorporated for illustration of preferred embodiments of the present invention and are not intended to limit the scope thereof.
SUMMARY OF THE INVENTION
[0025] In view of the foregoing  an embodiment herein provides a pressuring sensing device and a method of measuring the pressure of the fluid using the same. The pressure sensing device provided in accordance with the embodiments of the present invention features in that it is not only low cost  accurate  painless to miniaturize  and simple in construction  but also responds fast to changes in pressure  can measure vacuum pressure and is less prone to hysteresis. The pressure sensing device further features in that it has shape or geometry which is convenient to manufacture and do not need mechanical elements to digitize.
[0026] In accordance with the present invention  the pressure sensing device capable of sensing fluid pressure to which it is exposed comprises a substantially straight and cylindrical member comprising a first end and an opposite second end. The cylindrical member has a substantially circular inner hole or bore of suitable dimensions such that the inner hole has an open inlet at said first end of the cylindrical member to receive the fluid and blocked or blinded at the opposite second end. The inner hole extends throughout the length of the cylindrical member and is offset from a longitudinal central axis of the cylindrical member thereby defining a thin wall with thickness d1 and a thick wall with thickness d2  such that the relation d1 < d2 holds true  which makes the cross-section asymmetric.
[0027] In accordance with an embodiment a method of measuring the pressure of a fluid is provided using the pressure sensing device of the present invention. In accordance with this method the device described herein above is provided. The fluid  whose pressure is to be measured is allowed to enter through first end into the bore and thereafter the fluid is allowed to exert pressure thereby resulting in expansion of the thinner wall which is more as compared to that of the thicker wall thereby creating a deflection in the second end resulting of the cylindrical member which is because of curvature created in the cylindrical member  the curvature being created due to differential expansion of the walls and as well as the end moment created due to offset (eccentricity) of the bore axis with the neutral axis of the cylindrical member as a whole. The amount of deflection or curvature is measured and the pressure of the fluid may be calculated from the amount of deflection or curvature. Thus on application of fluid pressure inside the bore  the opposite second end of the cylindrical member is deflected from straight line due to differential expansion of the thin wall and the thick wall  wherein the thin wall expands more as compared to the thick wall.
[0028] In accordance with an alternative embodiment of the present invention  bellows with asymmetric cross section may be substituted partially or wholly for tubes. The bellows behave similar to the asymmetric tube but have higher flexibility and greater rate of expansion and bending under internal pressure.
[0029] In accordance with the present invention  as one of numerous possible applications  the pressure sensing device and in particularly the cylindrical member may be utilized just as pressure sensor or may be used as “artificial finger” in a robotic arm.
[0030] These and other aspects of the embodiments herein will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood  however  that the following descriptions  while indicating preferred embodiments and numerous specific details thereof  are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the embodiments herein without departing from the spirit thereof  and the embodiments herein include all such modifications.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] The detailed description is set forth with reference to the accompanying figures. In the figures. The use of the same reference numbers in different figures indicates similar or identical items.
[0032] FIG. 1a illustrates a cross-sectional view in a direction perpendicular to the longitudinal axis of the cylindrical member of the pressure sensing device in accordance with the embodiments of the present invention;
[0033] FIG. 1b illustrates a cut view in a direction parallel to the longitudinal axis of the cylindrical member of the pressure sensing device in accordance with the embodiments of the present invention;
[0034] FIG. 2a illustrates a top view of the pressure sensing device along with the pointer and scale for measuring the pressure of the fluid;
[0035] FIG. 2b illustrates a top view of the pressure sensing device  wherein the pressure sensing element or the cylindrical member is deflected on application of fluid pressure;
[0036] FIG. 3a illustrates an asymmetric flexible bellow  in accordance with an alternative embodiment of the present invention; and
[0037] FIG. 3b illustrates an asymmetric flexible bellow deflected on application of pressure  in accordance with an alternative embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0038] The embodiments herein and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments and detailed in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly  the examples should not be construed as limiting the scope of the embodiments herein.
[0039] As mentioned  there remains a need for developing a pressure sensing device capable of measuring the fluid pressure which is not only low cost  accurate  painless to miniaturize  and simple in construction  but also responds fast to changes in pressure  can measure vacuum pressure and is less prone to hysteresis.
[0040] Additionally  there is a need to have a pressure sensing device which have a shape or geometry which is convenient to manufacture and do not need mechanical elements to digitize.
[0041] The inventors of the present invention provide a pressure sensing device that is very simple in construction and is easy to manufacture.
[0042] In accordance with an embodiment of the present invention  a pressure sensing device is disclosed that overcomes the limitations of the prior art. The pressure sensing device of the present invention which is capable of sensing fluid pressure  to which it is exposed  the pressure sensing device essentially consists of a straight and cylindrical member having a first end and an opposite second end. The cylindrical member has a substantially circular inner hole or bore of suitable dimensions such that the bore has an open inlet at said first end of the cylindrical member to receive the fluid and blocked or blinded at the opposite second end. The inner hole extends throughout the length of the cylindrical member and is offset from a longitudinal central axis of the cylindrical member thereby defining a thin wall with thickness d1 and a thick wall with thickness d2  such that d1 is lesser than d2.
[0043] In accordance with the present invention the provision of the asymmetry in the position of the inner hole or the bore in the cylindrical member leads to a differential expansion of the walls when the fluid fills in the bore  wherein the fluid exerts pressures on the walls from inside. The differential expansion of the walls is responsible for the deflection of the cylindrical member leading to curvature in the cylindrical member and deflection of the opposite second end along with the bore  which is substantially circular  tending to become oval on application of the pressure.
[0044] In accordance with the present invention the amount of deflection from the original position may be correlated to the fluid pressure upon suitably calibrating the deflection. A pointer may be mounted on to the opposite second end of the cylindrical member to aid reading of the amount of deflection.
[0045] In accordance with the present invention the provision of a substantially straight and cylindrical member eliminates the complications related to manufacturing of the pressure sensing device  since it is simple to mold or cast straight tubes as compared to C shaped or curved tubes  the C shaped tubes being necessary for Bourdon tube type pressure sensing devices.
[0046] Now referring to FIG. 1a which illustrates the cross-sectional view in a direction perpendicular to the longitudinal axis of the cylindrical member 101 of the pressure sensing device 100 in accordance with the embodiments of the present invention. The cylindrical member 101 is provided with a bore 102 and the bore 102 is positioned asymmetrically in the cylindrical member with an offset with the longitudinal axis 101c of the cylindrical member  thereby the walls of the cylindrical member 101 has a thin wall having thickness d1 and indicated by numeral 101a and a thick wall having thickness d2 and indicated by numeral 101b.
[0047] In accordance with one embodiment of the present invention  the cylindrical member 101 is made of metals such stainless steel  Phosphor bronze  Beryllium Copper etc. Moreover  composite materials made of polymer and metallic material can also be used.
[0048] Now referring to FIG. 1b that illustrates the cut view in a direction parallel to the longitudinal axis of the cylindrical member 101 of the pressure sensing device 100 in accordance with the embodiments of the present invention. One end 103a  referred to as the first end hereinafter  of the cylindrical member 101 has an open inlet 103c to allow the fluid to enter into the bore 102. The other end 103b  referred to as the opposite second end  is blinded or closed so that the fluid entering the bore 102 through the open inlet 103c is retained in the bore 102 and exerts pressure onto the walls 101a and 101b of the cylindrical member.
[0049] FIG. 2a illustrates the pressure sensing device 100 along with the pointer 104 and scale 105 for measuring the pressure of the fluid under consideration. The cylindrical member 101 deflects [FIG. 2b] from the original position A to B on application of the fluid pressure inside the bore 102 owing to the differential expansion of the walls 101a and 101b. The pointer 104 along with the scale 105 which is calibrated indicate either the amount of deflection from which the value of the fluid pressure may be calculated or the scale may be suitably calibrated to read the fluid pressure directly.
[0050] FIG. 2b illustrates the pressure sensing device 100  wherein the pressure sensing element or the cylindrical member 101 is deflected on application of fluid pressure.
[0051] In accordance with an embodiment a method of measuring the pressure of a fluid 106 is provided using the pressure sensing device 100 of the present invention. The fluid 106  whose pressure is to be measured is allowed to enter into the bore 102 through first end 103a and thereafter the fluid 106 is allowed to exert pressure on the walls of the cylindrical member 101 thereby resulting in expansion of the thinner wall 101a more as compared to that of the thicker wall 101b thereby creating a deflection or curvature in the second end 103b resulting of the cylindrical member 101. The amount of deflection or curvature of second end is measured and the pressure of the fluid may be calculated from the amount of deflection or curvature. Thus on application of fluid pressure  the opposite second end 103b of the cylindrical member 101 is deflected from straight line and assumes a curved shape along with the bore 102 assuming an oval shape from the original circular shape  which is attributed to differential expansion of said thin wall and said thick wall.
[0052] In an alternative embodiment of the present invention  the asymmetric tube or the cylindrical member 101 with thin 101a and thick wall 101b can also be used gripping objects which can serve as a robotic hand. In accordance with this embodiment of the present invention  the robotic hand includes plurality of cylindrical members 101 that are configured as “fingers” of the robotic hand. On application of pressure by allowing fluid to pass into the bores 102 of the cylindrical members 101  the cylindrical members 101 are arranged such that all of the plurality of the cylindrical members 101  now acting as “fingers” bend so as to grip the object.
[0053] In accordance with the present invention  the robotic hand is operated by a pneumatic/ hydraulic system with a single internal chamber and controlled by a single motor. To apply desired fluid pressure  for each finger  the pressure is controlled independently through micro-valves.
[0054] In accordance with one embodiment one or more cylindrical members 101 may be attached to each other serially so that the bore 102 of each of the cylindrical members 101 may communicate the fluid and hence the fluid pressures to form a desired shape such as a curve or bow or any other suitable for specific application.
[0055] In accordance with one embodiment of the present invention  the bore 102 may have same or varying diameter through the entire length.
[0056] In accordance with one embodiment of the present invention  the shape of the bore may be chosen from a group of circular  oval  spherical  square or any other shape or combinations thereof.
[0057] In accordance with the embodiment of the present invention  the bore 102 may have a diameter that is varying periodically or non-periodically or follow a specific mathematical function or any combination of these to achieve a shape or design for specific application.
[0058] In accordance with one embodiment of the present invention  the position of the bore 102 in the cylindrical member may be same or may vary along the length of the cylindrical member 101  that is  the thickness d1 and d2 may remain same along the length of the cylindrical member 101 or may vary periodically or non-periodically or follow a specific mathematical function or any combination of these to achieve a shape or design for specific application.
[0059] In accordance with one embodiment of the present invention  bellows may be used as an alternative of tubes  as shown in FIG. 3a that illustrates an asymmetric flexible metallic bellow substituted for the tube. The bellow 301 with asymmetric cross section would behave similar to the asymmetric tube but would have higher flexibility and greater rate of expansion and bending under internal pressure. FIG. 3b illustrates the asymmetric flexible metallic bellow under pressure. In accordance with the embodiments of the present invention the bellows may be used to form finger joints in the robotic hand similar to the interphalangeal joints in human hand or to measure pressure.
[0060] In accordance with one embodiment of the present invention the pressure measured by the pressure sensing device may be converted into analog or digital or a hybrid signal by use of suitable mechanism for the conversion.
[0061] In accordance with one embodiment of the present invention the cylindrical member 101 is protected by a suitable cover such as a metal sheet. The cover may form a casing or the tube or bellow may be coated with suitable metal or any other material that protects the tube or bellow from external impacts.
[0062] Thus the present invention provides a pressure sensing device along with a method of measuring pressure of the fluid using the pressure sensing device.
[0063] In accordance with the present invention the provision of the substantially straight and cylindrical member 101  which is in form of tube or bellow reduces the cost pressure sensing device owning to convenience in manufacturing of the straight cylindrical member 101.
[0064] Thus  the pressure sensing device of the present invention has a geometry or shape which is suitable to manufacture at low cost.
[0065] In accordance with the present invention the pressure sensing device of the present invention is accurate  small and simple in construction as there is no need of providing any other mechanical elements as in case of Bourdon tube based pressure sensing device and the pressure sensing device can be digitized without any mechanical elements.
[0066] As the pressure sensing device comprises of the substantially straight and cylindrical member 101 which is essentially a tube or bellow with a bore that is offset with reference to the longitudinal axis of the cylindrical member 101  the miniaturization of the pressure sensing device is simple and straight forward  wherein only the dimensions of the tube or the cylindrical member 101 are to be decreased to a suitable scale.
[0067] In accordance with the present invention  the pressure sensing device may be used for measuring the vacuum pressure  wherein the deflection of the cylindrical member 101 would be in a direction opposite to that when it is pressurized by fluid.
[0068] In accordance with the present invention the pressure sensing device responds quickly to changes in the pressure because of differential expansion of the tube or bellow and the response time may be decreased by providing a cylindrical member 101 with a material that expands and contracts quickly.
[0069] In accordance with the present invention  the pressure sensing device is less prone to hysteresis as the original shape of the cylindrical member 101 is substantially straight tube or bellow as compared to the Bourdon tube which has C shape.
[0070] Though the present invention has been described using the specific shapes of the “cylindrical member”  “bore” or “inner hole” or “tube” or “bellow” or “metallic tube” or “metallic bellows”  it is evident that any other shapes or equivalent forms or combination thereof may be used and the present invention is not limited by these specific shapes. Further the material of make  for the tube and bellow  is metal. It should be noted that any other material that expand on application of pressure may be utilized instead of metal. The material of make may be metal  semi metal  alloy or composite materials made of polymer or plastic or rubber with metals. It is to be noted that any other material than described herein above may be used provided the material has low hysteresis  can withstand pressures to be measured and expand somewhat in linear manner with pressure changes.
[0071] The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can  by applying current knowledge  readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept  and  therefore  such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore  while the embodiments herein have been described in terms of preferred embodiments  those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.

Abstract:
A pressure sensing device 100 capable of sensing fluid pressure to which it is exposed is disclosed the device comprising a substantially straight-cylindrical member 101 comprising a first end 103a and an opposite second end 103b. The cylindrical member 101 is provided with a circular inner hole or bore 102 of suitable dimensions such that the bore 102 has an open inlet 103c at said first end 103a of the cylindrical member 101 to receive the fluid 106 and blocked or blinded at the opposite second end 103b and bore 102 extends throughout the length of the cylindrical member 101. The bore 102 is featured in that it is offset from a longitudinal axis 101c of the cylindrical member 101 thereby defining a thin wall 101a with thickness d1 and a thick wall 101b with thickness d2  such that the relation d1 < d2 holds true  thereby defining a asymmetric tube  wherein said device works on principle of differential expansion of the asymmetric tube and the end moment induced due to asymmetry of cross-section for sensing and measuring pressure of a fluid under consideration. A method of measuring fluid pressure using the pressure sensing device is also disclosed.

We Claim:
1. A device 100 capable of sensing fluid pressure to which it is exposed said device 100 comprising:
a substantially straight and cylindrical member 101 comprising a first end 103a and an opposite second end 103b;
said cylindrical member 101 having a bore 102  said bore 102 having an open inlet 103c at said first end of said cylindrical member 101 to receive fluid 106 and blinded at said opposite second end 103b;
said bore 102 is provided such that it extends within said cylindrical member 101 offset from a longitudinal axis 101c of the cylindrical member 101  thereby defining a thin wall 101a with thickness d1 and a thick wall 101b with thickness d2  wherein d1 < d2.
2. The device 100 as claimed in claim 1  wherein said cylindrical member 101 is in form of a tube or bellow or any combination thereof.
3. The device 100 as claimed in claim 1  wherein on application of fluid pressure  the opposite second end 103b of said cylindrical member 101 is deflected from straight line owing to differential expansion of said thin wall 101a and said thick wall 101b.
4. The device 100 as claimed in claim 1  wherein on application of fluid pressure  the opposite second end 103b of said cylindrical member 101 gets deflected from straight line  wherein said thin wall 101a being stretched more as compared with the stretching of said thick wall 101b defining a curvature of said cylindrical member 101.
5. The device 100 as claimed in claim 1  wherein the said cylindrical member 101 is substantially circular.
6. The device 100 as claimed in claim 1  wherein said bore 102 is chosen from a group of shapes including circular  oval  triangular  square  rectangular polygon or combination thereof.
7. The device 100 as claimed in claim 1  wherein said cylindrical member 101 assumes an oval shape on application of fluid pressure.
8. The device 100 as claimed in any of the preceding claims  wherein said cylindrical member 101 is made of metal or alloys or composite material  wherein the metal is selected from the group of metals including stainless steel  Phosphor bronze  and Beryllium Copper.
9. A device capable of being used as a robot gripper for pick and place operation on application of a suitable fluid pressure to which it is exposed  said device comprising:
at least one cylindrical member 101  said cylindrical member 101 comprising a first end 103a and an opposite second end 103b; a substantially circular bore 102  said bore 102 having an open inlet 103c at said first end 103a of said cylindrical member 101 to receive fluid 106 and blinded at said opposite second end 103b; said bore 102 is provided such that it extends within said cylindrical member 101 in a manner offset from a longitudinal axis 101c of said cylindrical member 101  thereby defining a thin wall 101a with thickness d1 and a thick wall 101b with thickness d2  wherein d1 < d2; and
said at least one cylindrical member 101 being configured to grip an object on application of fluid pressure.
10. A method of measuring the pressure of a fluid is provided  said method comprising:
providing a device 100 capable of sensing fluid pressure to which it is exposed  said device 100 comprising:
a substantially straight and cylindrical member 101 comprising a first end 103a and an opposite second end 103b;
said cylindrical member 101 having a bore 102  said bore 102 having an open inlet 103c at said first end 103a of said cylindrical member 101 to receive fluid 106 and blinded at said opposite second end 103b;
said bore 102 is provided such that it extends within said cylindrical member 101 in a manner offset from a longitudinal axis 101c of the cylindrical member 101  thereby defining a thin wall 101a with thickness d1 and a thick wall 101b with thickness d2  wherein d1 < d2;
allowing a fluid 106  whose pressure is to be measured  to enter through open inlet 103c into said bore 102;
allowing said fluid 106 to exert pressure on walls 101a and 101b thereby expanding said thinner wall 101a more as compared to that of said thicker wall 101b thereby allowing deflection of said second end 103b resulting in creation of a curvature in said straight cylindrical member 101; and
measuring amount of deflection of second end 103b and calculating pressure of said fluid 106 from the amount of deflection.