EP0380762B1 - Current to pressure transducer employing magnetic fluid with self-correcting nozzle - Google Patents
Current to pressure transducer employing magnetic fluid with self-correcting nozzle Download PDFInfo
- Publication number
- EP0380762B1 EP0380762B1 EP19890119767 EP89119767A EP0380762B1 EP 0380762 B1 EP0380762 B1 EP 0380762B1 EP 19890119767 EP19890119767 EP 19890119767 EP 89119767 A EP89119767 A EP 89119767A EP 0380762 B1 EP0380762 B1 EP 0380762B1
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- European Patent Office
- Prior art keywords
- current
- magnetic
- nozzle
- diaphragm
- pressure transducer
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- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
- F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
- F15B5/00—Transducers converting variations of physical quantities, e.g. expressed by variations in positions of members, into fluid-pressure variations or vice versa; Varying fluid pressure as a function of variations of a plurality of fluid pressures or variations of other quantities
- F15B5/003—Transducers converting variations of physical quantities, e.g. expressed by variations in positions of members, into fluid-pressure variations or vice versa; Varying fluid pressure as a function of variations of a plurality of fluid pressures or variations of other quantities characterised by variation of the pressure in a nozzle or the like, e.g. nozzle-flapper system
Definitions
- This invention relates to the regulation of air pressure in response to electrical signals and in particular to a transducer for converting an electrical current to a corresponding pressure in a system that uses compressed air.
- the invention also relates to a nozzle that is useful with the current-to-pressure transducer and in particular to a self-correcting nozzle structure.
- Compressed air is used in many systems for controlling machinery because compressed air is immune to electrical interference and is safe in explosive environments. Compressed air is generally used, for example, to control valves and other mechanical devices in industrial systems.
- sensors are generally provided that generate small electrical currents, in the range of 4 to 20 milliamperes, for example. These currents are used to establish a corresponding pressure of the compressed air and to provide a sufficient volume of pressurized air for accomplishing the desired mechanical task.
- the conversion from electrical current to a corresponding pressure is accomplished by use of a current-to-pressure transducer that is capable of regulating the pressure of a small volume of air, wherein the volume of air is amplified by using standard pneumatic amplifiers.
- a nozzle In the conventional current-to-pressure transducer, a nozzle is supplied that directs compressed air to the atmosphere at a rate determined by the proximity of a flapper valve to a nozzle orifice.
- the flapper valve is generally mounted on a rotating suspension and is rotated by magnetic forces that are generated by an electromagnet. The flapper is rotated toward the nozzle so that the air that escapes to the atmosphere is reduced.
- Such prior art devices are formed as delicate mechanical assemblies that require several adjustments during fabrication and are relatively expensive to produce.
- a nozzle is a converging or converging-diverging tube attached to the outlet of a pipe, hose or pressure chamber.
- the purpose of the nozzle is to convert the pressure existing in a fluid into velocity efficiently.
- a nozzle allows a pressure to be carried in a pipe or hose adjacent to the nozzle.
- nozzles used for controlling air flow generally terminate with an outer diameter slightly larger than the inner diameter.
- the outer diameter of a nozzle would be 0.035 inch (0,89 mm) and the inner diameter would be 0.026 inch (0,66 mm), by way of example.
- the current-to-pressure transducers that use such type nozzles usually incorporate a flapper, which is a pivotable paddle-shaped part, or a diaphragm to vary the flow of air through the nozzle. In either case, it is necessary that a good seal be provided at the end of the transducer from which there is the high flow of air or fluid.
- the flapper or diaphragm In order to achieve the required good seal, the flapper or diaphragm must be precisely aligned in a plane that is perpendicular to the axis of the nozzle. If the alignment is not proper, the flapper or diaphragm will first strike an edge of the nozzle end and will not advance further towards making an effective complete seal. It is relatively difficult to provide the desired orthogonal alignment of the flapper or diaphragm in a planar orientation relative to the nozzle axis.
- the generic U.S. Patent 4,579,137 describes a transducer including a membrane 22 on which a magnetic button 22A is positioned.
- the air gap between the button 22A and a magnetic part 14 in which a port 24 is formed increases in size.
- the sum of the air gaps between the button 22A and the magnetic part 14, and between the button 22A and the post 12 remains constant.
- the undesirable air gap between button 22A and the magnetic part 14 adversely affects the efficiency of the magnetic circuit and consequently impairs the proper control of the air pressure in the patented device.
- U.S. Patent 4,053,952 describes the use of a magnetic fluid for occluding a tube that is disposed within the body of a human.
- the patented device used no moving parts in the mechanism, which serves as a valve or a pump selectively.
- the patent states that when the magnetic field of the permanent magnets is present, the pressure of the magnetic fluid forces the membrane against a pole piece thus occluding the flow passage (column 5, lines 34-37).
- the patented device serves as an on-off valve or pump, but does not act to vary the size of an air gap in response to an input current that varies the strength of a magnetic field in selected regions of a magnetic fluid.
- a bucking magnetic field is required to counteract the magnetic field from the permanent magnet (col.4, line 11-17) which surrounds the portion of the tube that is to be affected by the pressure which the patent alleges occurs in the magnetic fluid.
- the patent does not teach how to move a membrane by using a magnetic fluid, and assumes (as shown in Fig. 2) that an essentially uniform magnetic field acting on the entire volume of magnetic fluid creates a pressure within that fluid to cause displacement of a membrane.
- the patented device requires compression or expansion of the fluid, or the generation of regions of vacuum within the chamber containing the magnetic fluid in order for his device to be operable.
- An object of this invention is to provide a current-to-pressure transducer that regulates the air pressure within an air supply line so that the pressure differential between this line and ambient air pressure varies substantially linearly with an applied electrical current.
- pressure will be used to mean the pressure relative to the environment.
- Another object of this invention is to provide a transducer that is relatively efficient and has uniform characteristics so that individual adjustments need not be made.
- Another object is to provide a current-to-pressure transducer that can be mass produced at low cost.
- a further object is to provide a current-to-pressure transducer that is immune to electrical interference and is safe in explosive environments.
- Another object of this invention is to provide a nozzle and pole piece structure that affords an effective complete seal at the nozzle end from which fluid or air flows to the ambient environment.
- Another object of this invention is to provide an integral nozzle and pole piece structure which is easier to manufacture than prior known nozzles of this type.
- a current-to-pressure transducer incorporates a magnetic fluid that is in contact with a flexible membrane or diaphragm.
- the diaphragm responds to forces exerted on the magnetic fluid and moves towards a nozzle to narrow the space through which the air flowing from the nozzle is passed to the ambient environment.
- the diaphragm moves in accordance with an electrical input current.
- the current is applied to a coil wound around a magnetic circuit that moves the flexible membrane towards the nozzle by means of the magnetic fluid. Movement of the membrane towards the nozzle decreases the flow of air from the nozzle and increases the pressure of the air within the air supple line.
- pressure sensing means and electronic feedback are used to achieve the desired linearity between the pressure within the line supplying air to the nozzle and the electrical input current.
- Another feature of this invention is a self-correcting nozzle and pole piece structure that is useful with a current-to-pressure transducer is formed from an integral piece of magnetic material.
- the nozzle and pole piece structure is formed so that the respective ends of the nozzle and pole piece which face the sealing element, which in this case is a flexible diaphragm, are coplanar.
- the nozzle structure provides a self-correcting feature that compensates for any canting or misalignment of the diaphragm. Slots are provided at the end of the integral piece facing the diaphragm to allow the escape of excess air.
- the current-to-pressure transducer of this invention receives compressed air from a pneumatic amplifier 32.
- the current-to-pressure transducer includes an air supply line 24 having a nozzle 10 at one end and is coupled at the other end to the pneumatic amplifier 32.
- a baseplate 19 made of magnetically soft material is joined to a magnetic member 20 by a screw 37 or other suitable means.
- a magnetic member 21 is attached to the member 20 by a screw 38 or other attachment means.
- a cylindrical magnetic member 22 is positioned in contact with and partly within an aperture of the magnetic member 21. As illustrated in Fig. 4, a pole piece 11 is provided at the upper end of the tubular member 22.
- the baseplate 19 is formed with two chambers 14 and 16 that are connected by a capillary tube 15.
- a magnetic fluid 30 which may be a colloidal suspension of magnetic particles in a nonmagnetic carrier, such as Ferrofluid (a trademark of Ferrofluidics Corporation, Nashua, New Hampshire) is provided to chambers 14 and 16 and the capillary tube 15.
- the magnetic fluid 30 may also be any composite, noncolloidal material that is not capable of supporting shear forces and that exhibits a magnetic susceptibility.
- a plug 18 is provided to enable filling the capillary tube 15 and chambers 14 and 16 with magnetic fluid 30.
- a coil 23 is wound around a portion of the magnetic member 22.
- Baseplate 19, magnetic members 20, 21, 22, the gap between pole piece 11 and the magnetic fluid 30 in chamber 14 and the magnetic fluid 30 in chamber 14 form a magnetic circuit.
- current is applied to the coil 23, the magnitude of the magnetic flux at the pole piece 11 is varied in accordance with the magnitude of the current signal.
- flexible membranes or diaphragms 13 and 17 are located respectively at the lower open ends of the chambers 14 and 16 to seal the ends of the chambers and to contain the magnetic fluid 30 within the chambers.
- the flexible membranes 13 and 17 are retained by a nonmagnetic retainer element or ring 25 which abuts the diaphragms.
- the element 25 is fastened at its exposed surface to the baseplate 19 by screws or other suitable means.
- the pneumatic amplifier 32 provides compressed air through the air supply line 24 to the nozzle 10.
- the air passes through the space between the diaphragm 13 and the surface of the nozzle 10. Escape holes 12 or other suitable means are provided in the upper portion of the magnetic member 22, as shown in Fig. 4 to prevent undesirable pressure build up between the pole piece 11 and diaphragm 13.
- An air pressure sensor 26 senses the pressure of the compressed air that is passing through the air supply line 24 and generates a signal representative of the pressure value.
- the signal is provided to an electronic feedback circuit 27, which also receives the input current through lead 34.
- the input current and the signal representative of the pressure value are compared in the circuit 27 and a current representative of this comparison is provided to the coil 23.
- the electronic feedback circuit 27 adjusted the actual current to the coil 23 so that the pressure in the air line 24 is substantially linear with the input current.
- the input current during operation maintains the coil in an excited state and as a result the pole piece 11 distributes magnetic flux in the area adjacent to the diaphragm 13.
- the magnitude of the magnetic flux emanating from the pole piece 11 varies with variations in the current supplied to the coil 23.
- the magnetic fluid 30 in chamber 14 is attracted towards the pole piece 11 and the diaphragm 13 is deformed to an extent directly related to the magnitude of the current which is applied to the coil 23.
- the diaphragm 13 deforms and moves partially towards the pole piece 11 so that the space between the diaphragm 13 and the nozzle 10 decreases.
- the pressure of air within the air line 24 supplying air to the nozzle 10 is increased.
- the volume of magnetic fluid that is displaced in chamber 14 associated with the displacement of diaphragm 13 is provided from chamber 16 to chamber 14.
- the diaphragm 17 moves inwardly to the chamber 16 in an equal and opposite direction to diaphragm 13.
- the air supply line 24 including the nozzle 10 is located under the chamber 16.
- the coil 23 and the associated magnetic members 20, 21, 22, baseplate 19 and pole piece 11 remain in association with the chamber 14 for coaction with the diaphragm 13.
- An increase in current to the coil 23 causes the diaphragm 13 to deform toward the pole piece 11 and the volume of magnetic fluid that is displaced from chamber 16 to chamber 14 causes the diaphragm 17 to move away from the nozzle 10. Consequently, the pressure of the air in line 24 is decreased.
- the air line 24 is made of nonmagnetic material such as aluminum, or alternatively is magnetically isolated from the magnetic circuit which includes the coil 23 and the magnetic member 31, inter alia.
- a feature of this invention is the insensitivity to gravitational or acceleration forces. Because the magnetic fluid 30 is relatively incompressible, the diaphragms 13 and 17 move equally in opposite directions. In those embodiments in which the diaphragms are coplanar, the transducer is insensitive to forces that are applied perpendicularly to the plane of the diaphragms. The transducer is relatively insensitive to forces that are applied perpendicularly to the plane of the drawing and a line through the centers of the chambers, irrespective of whether the diaphragms are coplanar. Also the viscous damping that is associated with transport of the fluid 30 through the capillary 15 causes the transducer to be insensitive to shock in any direction. The damping is enhanced as the viscosity of the magnetic fluid 30 is increased and the conductance of the capillary 15 is decreased. Damping also can be used to limit the high frequency response of the transducer.
- a further increase in sensitivity is achieved by affixing an element 28 made of a solid, magnetically soft material, such as iron, to the center of the diaphragm 13.
- the element 28 is disposed within the magnetic fluid in chamber 24 and has a higher saturation magnetization than the magnetic fluid.
- the element 28 also can provide stiffness to the central portion of the diaphragm.
- an element 29 is located in the chamber 16 and is affixed to the diaphragm 17.
- the element 29 may be substantially identical to the element 28,or may be of a nonmagnetic material with suitable size and shape to achieve the desired insensitivity.
- Fig. 5 is a curve representing the changes in pressure (psi) as a function of current (milliamps).
- a 450 Gauss, 400 cp Ferrofluid was used.
- the element 28 is a steel slug of 3/8-inch (9,52 mm) diameter and 3/16-inch (4,76 mm) long cemented to the diaphragm 13 with RTV silicone sealant.
- the air supply pressure is 18 psi (1,22 atm). It should be understood that these parameters, materials and dimensions are exemplary and the invention is not limited thereby.
- the transducer comprises a single chamber and a single flexible diaphragm.
- an air space is provided above the level of the magnetic fluid to allow displacement of the diaphragm.
- nozzle 10 is made of magnetic material and functions also as pole piece 11.
- the outer coaxial member 11 and holes 12 shown in Figure 4 are eliminated.
- the novel current-to-pressure transducer disclosed herein employs a magnetic fluid to coact with flexible diaphragms disposed in close juxtaposition to a nozzle of an air line.
- the transducer lends itself to mass production and low cost, is efficient in operation, and does not require individual adjustments.
- a nozzle and pole piece structure that is formed from a rod 40 made of a magnetic material, such as Carpenter High Permeability "49" Alloy, for example.
- the rod 40 has a diameter of about 3/16 inch (4,76 mm) in this particular embodiment.
- the magnetic rod 40 is formed with functional pole pieces 41 at a slotted end of the rod 40. Slots 43 allow the escape of excess air and are relatively easy to machine, with saw blades or slot cutters, as compared to the formation of individual bleed holes 12 and the associated deep circumferential groove between elements 10 and 11 to which the holes connect, shown in Fig. 2.
- the pole pieces 41 provide magnetic flux for coaction with electric current flowing through the electrical coil (not shown) of the electromagnetic circuit. Application of electric current to the coil causes the magnetic fluid 30 to move which, in turn, causes the deformation of the flexible diaphragm as explained heretofore thereby controlling air flow through the nozzle .
- the rod 40 has a threaded part 42 for engagement with a threaded cap 44 of a housing assembly, shown in Fig. 9.
- the rod 40 also has a hexagonal part 47 formed at the end adjacent to the threaded part 42 to allow the rod to be turned so that the height of the nozzle relative to the diaphragm can be adjusted for proper operation, and locked with nut 68.
- Figure 7 shows an end view of the nozzle and pole piece structure 40 viewed from the slotted end.
- the rod 40 is formed with one or more of the longitudinal slots 43, which extend inwardly to at least the outer diameter of a relatively shallow groove 46 formed within the end of the rod 40.
- the slots 43 serve the same purpose as the holes 12 depicted in Fig. 2 to allow the escape of excess air, but are easier to machine and fabricate than the transverse holes. Groove 46 may be eliminated if the slots 43 extend inward to the proximity of the constricted passage 49.
- an open channel is formed within the interior of the nozzle tube 48 to allow the passage and escape of air.
- the nozzle tube 48 may be tapered at the end portion that faces the diaphragm so that a constricted passage 49 is formed at the end of the nozzle channel 48.
- the constricted portion 49 of the channel 48 reduces the volume of air that escapes from the nozzle at a given pressure.
- the amount of air flow from the channel portion 49 is regulated by the position of the diaphragm 13, which is controlled by the action of the magnetic fluid in response to the electric current supply to the coil of the electromagnetic circuit.
- Fig. 9 shows the main housing 50 for the integral nozzle and pole piece structure which is made of soft iron.
- Diaphragms 52 and 54 are spaced by a soft iron spacer 56 formed with magnetic fluid chambers 58 and 60.
- O-ring seals 62 and 64 are provided with the chambers.
- a threaded aluminum retainer 66 is located adjacent to the diaphragm 54 for connection to the spacer 56.
- a lock nut 67 is located against the retainer 66 and four cap screws 70 tie the spacer 56 and retainer 66 with the diaphragms 52 and 54 to the main housing 50.
- a second nozzle (not shown) may be threaded into retainer 66 to coact with diaphragm 54.
- the threaded element 44 which is made as a soft iron cap with internal threads for engaging the nozzle, is joined with a lock nut 68 by means of four Allen socket cap screws 72 to the main housing 50.
- Fig. 10 depicts the assembled unit which has a notch 74 in the housing 50 to allow connection of electrical circuitry to the electrical coil of the electromagnetic circuit and to permit escape of excess air.
- the end of the nozzle tube 46 and the end of the pole piece 41 are substantially coplanar.
- the lower surface of the diaphragm conforms to the shape of the pole piece 41. Since the alignment of the ends of the pole piece 41 and nozzle tube 46 are in substantial planar alignment, the diaphragm will provide a complete seal at the face of the nozzle.
- any canting of the diaphragm 13 is self-corrected because the force on the diaphragm acts between a point of first contact of the diaphragm 13 with the end of the larger diameter pole piece 41 and the coplanar end of the nozzle tube.
- the integral nozzle and pole piece structure also is easier to fabricate with the slots 44 formed at the end of the rod structure to allow the desired air escape instead of with transverse holes as used in prior nozzle assemblies.
- Such transverse holes either require a difficult process to machine a deep groove between the nozzle 10 and pole piece 11, or require fabricating the nozzle 10 and pole piece 11 separately, in which case it would be difficult to assemble these parts to achieve the desired coplanarity.
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- Engineering & Computer Science (AREA)
- Physics & Mathematics (AREA)
- Fluid Mechanics (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Supply Devices, Intensifiers, Converters, And Telemotors (AREA)
- Nozzles (AREA)
- Reciprocating Pumps (AREA)
Description
- This invention relates to the regulation of air pressure in response to electrical signals and in particular to a transducer for converting an electrical current to a corresponding pressure in a system that uses compressed air. The invention also relates to a nozzle that is useful with the current-to-pressure transducer and in particular to a self-correcting nozzle structure.
- Compressed air is used in many systems for controlling machinery because compressed air is immune to electrical interference and is safe in explosive environments. Compressed air is generally used, for example, to control valves and other mechanical devices in industrial systems. When using compressed air in a system, sensors are generally provided that generate small electrical currents, in the range of 4 to 20 milliamperes, for example. These currents are used to establish a corresponding pressure of the compressed air and to provide a sufficient volume of pressurized air for accomplishing the desired mechanical task. In some systems, the conversion from electrical current to a corresponding pressure is accomplished by use of a current-to-pressure transducer that is capable of regulating the pressure of a small volume of air, wherein the volume of air is amplified by using standard pneumatic amplifiers. In the conventional current-to-pressure transducer, a nozzle is supplied that directs compressed air to the atmosphere at a rate determined by the proximity of a flapper valve to a nozzle orifice. The flapper valve is generally mounted on a rotating suspension and is rotated by magnetic forces that are generated by an electromagnet. The flapper is rotated toward the nozzle so that the air that escapes to the atmosphere is reduced. Such prior art devices are formed as delicate mechanical assemblies that require several adjustments during fabrication and are relatively expensive to produce.
- A nozzle is a converging or converging-diverging tube attached to the outlet of a pipe, hose or pressure chamber. The purpose of the nozzle is to convert the pressure existing in a fluid into velocity efficiently. A nozzle allows a pressure to be carried in a pipe or hose adjacent to the nozzle.
- Presently known nozzles used for controlling air flow generally terminate with an outer diameter slightly larger than the inner diameter. Typically, the outer diameter of a nozzle would be 0.035 inch (0,89 mm) and the inner diameter would be 0.026 inch (0,66 mm), by way of example. The current-to-pressure transducers that use such type nozzles usually incorporate a flapper, which is a pivotable paddle-shaped part, or a diaphragm to vary the flow of air through the nozzle. In either case, it is necessary that a good seal be provided at the end of the transducer from which there is the high flow of air or fluid. In order to achieve the required good seal, the flapper or diaphragm must be precisely aligned in a plane that is perpendicular to the axis of the nozzle. If the alignment is not proper, the flapper or diaphragm will first strike an edge of the nozzle end and will not advance further towards making an effective complete seal. It is relatively difficult to provide the desired orthogonal alignment of the flapper or diaphragm in a planar orientation relative to the nozzle axis.
- The generic U.S. Patent 4,579,137 describes a transducer including a
membrane 22 on which a magnetic button 22A is positioned. When the magnetic button is attracted to a post 12B, the air gap between the button 22A and amagnetic part 14 in which aport 24 is formed increases in size. The sum of the air gaps between the button 22A and themagnetic part 14, and between the button 22A and thepost 12 remains constant. The undesirable air gap between button 22A and themagnetic part 14 adversely affects the efficiency of the magnetic circuit and consequently impairs the proper control of the air pressure in the patented device. - U.S. Patent 4,053,952 describes the use of a magnetic fluid for occluding a tube that is disposed within the body of a human. The patented device used no moving parts in the mechanism, which serves as a valve or a pump selectively. The patent states that when the magnetic field of the permanent magnets is present, the pressure of the magnetic fluid forces the membrane against a pole piece thus occluding the flow passage (column 5, lines 34-37). The patented device serves as an on-off valve or pump, but does not act to vary the size of an air gap in response to an input current that varies the strength of a magnetic field in selected regions of a magnetic fluid. In the patent, a bucking magnetic field is required to counteract the magnetic field from the permanent magnet (col.4, line 11-17) which surrounds the portion of the tube that is to be affected by the pressure which the patent alleges occurs in the magnetic fluid. The patent does not teach how to move a membrane by using a magnetic fluid, and assumes (as shown in Fig. 2) that an essentially uniform magnetic field acting on the entire volume of magnetic fluid creates a pressure within that fluid to cause displacement of a membrane. The patented device requires compression or expansion of the fluid, or the generation of regions of vacuum within the chamber containing the magnetic fluid in order for his device to be operable. As illustrated in Figure 2 of the patent, if the
membrane 38 were to move either the volume ofmagnetic fluid 28 would have to increase, or a region of vacuum would have to be created within the chamber containing thefluid 28. The compressibility of fluids is such that the change in volume is negligible and any region of vacuum would be opposed by the ambient or atmospheric pressure to which the contents of thereservoir 14 are vented. The atmospheric pressure that is transmitted through themembrane 38 to the magnetic fluid at all times is greater than any pressure that can be generated by magnetic means. Therefore thediaphragm 38 described in the patent does not move. - It is highly desirable to employ a simple current-to-pressure transducer that lends itself to facile production at low cost without the need for individual mechanical adjustments.
- An object of this invention is to provide a current-to-pressure transducer that regulates the air pressure within an air supply line so that the pressure differential between this line and ambient air pressure varies substantially linearly with an applied electrical current. Henceforth, the word "pressure" will be used to mean the pressure relative to the environment.
- Another object of this invention is to provide a transducer that is relatively efficient and has uniform characteristics so that individual adjustments need not be made.
- Another object is to provide a current-to-pressure transducer that can be mass produced at low cost.
- A further object is to provide a current-to-pressure transducer that is immune to electrical interference and is safe in explosive environments.
- Another object of this invention is to provide a nozzle and pole piece structure that affords an effective complete seal at the nozzle end from which fluid or air flows to the ambient environment.
- Another object of this invention is to provide an integral nozzle and pole piece structure which is easier to manufacture than prior known nozzles of this type.
- In accordance with this invention, a current-to-pressure transducer incorporates a magnetic fluid that is in contact with a flexible membrane or diaphragm. The diaphragm responds to forces exerted on the magnetic fluid and moves towards a nozzle to narrow the space through which the air flowing from the nozzle is passed to the ambient environment. The diaphragm moves in accordance with an electrical input current. The current is applied to a coil wound around a magnetic circuit that moves the flexible membrane towards the nozzle by means of the magnetic fluid. Movement of the membrane towards the nozzle decreases the flow of air from the nozzle and increases the pressure of the air within the air supple line. In one embodiment pressure sensing means and electronic feedback are used to achieve the desired linearity between the pressure within the line supplying air to the nozzle and the electrical input current.
- Another feature of this invention is a self-correcting nozzle and pole piece structure that is useful with a current-to-pressure transducer is formed from an integral piece of magnetic material. The nozzle and pole piece structure is formed so that the respective ends of the nozzle and pole piece which face the sealing element, which in this case is a flexible diaphragm, are coplanar. The nozzle structure provides a self-correcting feature that compensates for any canting or misalignment of the diaphragm. Slots are provided at the end of the integral piece facing the diaphragm to allow the escape of excess air.
- The invention will be described in greater detail with reference to the drawing in which:
- Figure 1 is a side cross-sectional view of a current-to-pressure transducer, made in accordance with this invention;
- Figure 2 is a side cross-sectional view of an alternative implementation of the current-to-pressure transducer of this invention;
- Figure 3 is a cross-sectional view, partly broken away, of another implementation of the invention/
- Figure 4 is an enlarged isometric view, partly broken away, showing the relationship of a
pole piece 11 to thenozzle 10 and the nozzleair supply line 24, as used in the transducer of this invention; - Figure 5 is a representative curve plotting pressure against current without electronic feedback to aid in the explanation of the operation of the current-to-pressure transducer;
- Figure 6 is a side view of a nozzle and pole piece, made in accordance with this invention;
- Figure 7 is an end view at the slotted end of the nozzle and pole piece structure, such as illustrated in Fig. 6;
- Figure 8A is an enlarged cross-sectional view, partly broken away, taken across lines A-A′ of Fig. 7;
- Figure 8B is an enlarged cross-sectional view, partly broken away, taken across lines B-B′ of Fig. 7;
- Figure 9 is an exploded view of an assembly drawing illustrating the housing which encloses the nozzle and pole piece structure; and
- Figure 10 s an isometric view illustrating an assembled housing which encloses the nozzle and pole piece structure of this invention.
- With reference to Fig. 1, the current-to-pressure transducer of this invention receives compressed air from a
pneumatic amplifier 32. The current-to-pressure transducer includes anair supply line 24 having anozzle 10 at one end and is coupled at the other end to thepneumatic amplifier 32. - A
baseplate 19 made of magnetically soft material is joined to amagnetic member 20 by ascrew 37 or other suitable means. Amagnetic member 21 is attached to themember 20 by ascrew 38 or other attachment means. A cylindricalmagnetic member 22 is positioned in contact with and partly within an aperture of themagnetic member 21. As illustrated in Fig. 4, apole piece 11 is provided at the upper end of thetubular member 22. - The
baseplate 19 is formed with twochambers capillary tube 15. In keeping with this invention, amagnetic fluid 30 which may be a colloidal suspension of magnetic particles in a nonmagnetic carrier, such as Ferrofluid (a trademark of Ferrofluidics Corporation, Nashua, New Hampshire) is provided tochambers capillary tube 15. Themagnetic fluid 30 may also be any composite, noncolloidal material that is not capable of supporting shear forces and that exhibits a magnetic susceptibility. Aplug 18 is provided to enable filling thecapillary tube 15 andchambers magnetic fluid 30. - A
coil 23 is wound around a portion of themagnetic member 22.Baseplate 19,magnetic members pole piece 11 and themagnetic fluid 30 inchamber 14 and themagnetic fluid 30 inchamber 14 form a magnetic circuit. When current is applied to thecoil 23, the magnitude of the magnetic flux at thepole piece 11 is varied in accordance with the magnitude of the current signal. - In accordance with this invention, flexible membranes or
diaphragms chambers magnetic fluid 30 within the chambers. Theflexible membranes ring 25 which abuts the diaphragms. Theelement 25 is fastened at its exposed surface to thebaseplate 19 by screws or other suitable means. - In operation, the
pneumatic amplifier 32 provides compressed air through theair supply line 24 to thenozzle 10. The air passes through the space between thediaphragm 13 and the surface of thenozzle 10. Escape holes 12 or other suitable means are provided in the upper portion of themagnetic member 22, as shown in Fig. 4 to prevent undesirable pressure build up between thepole piece 11 anddiaphragm 13. Anair pressure sensor 26 senses the pressure of the compressed air that is passing through theair supply line 24 and generates a signal representative of the pressure value. The signal is provided to anelectronic feedback circuit 27, which also receives the input current throughlead 34. The input current and the signal representative of the pressure value are compared in thecircuit 27 and a current representative of this comparison is provided to thecoil 23. Theelectronic feedback circuit 27 adjusted the actual current to thecoil 23 so that the pressure in theair line 24 is substantially linear with the input current. The input current during operation maintains the coil in an excited state and as a result thepole piece 11 distributes magnetic flux in the area adjacent to thediaphragm 13. The magnitude of the magnetic flux emanating from thepole piece 11 varies with variations in the current supplied to thecoil 23. Themagnetic fluid 30 inchamber 14 is attracted towards thepole piece 11 and thediaphragm 13 is deformed to an extent directly related to the magnitude of the current which is applied to thecoil 23. Thediaphragm 13 deforms and moves partially towards thepole piece 11 so that the space between thediaphragm 13 and thenozzle 10 decreases. As a result, the pressure of air within theair line 24 supplying air to thenozzle 10 is increased. During the deformation of thediaphragm 13 resulting from themagnetic fluid 30 being moved towards thepole piece 11, the volume of magnetic fluid that is displaced inchamber 14 associated with the displacement ofdiaphragm 13 is provided fromchamber 16 tochamber 14. Thediaphragm 17 moves inwardly to thechamber 16 in an equal and opposite direction to diaphragm 13. - With reference to Fig. 2, the
air supply line 24 including thenozzle 10 is located under thechamber 16. Thecoil 23 and the associatedmagnetic members baseplate 19 andpole piece 11 remain in association with thechamber 14 for coaction with thediaphragm 13. An increase in current to thecoil 23 causes thediaphragm 13 to deform toward thepole piece 11 and the volume of magnetic fluid that is displaced fromchamber 16 tochamber 14 causes thediaphragm 17 to move away from thenozzle 10. Consequently, the pressure of the air inline 24 is decreased. In this embodiment of Fig. 2, theair line 24 is made of nonmagnetic material such as aluminum, or alternatively is magnetically isolated from the magnetic circuit which includes thecoil 23 and themagnetic member 31, inter alia. - A feature of this invention is the insensitivity to gravitational or acceleration forces. Because the
magnetic fluid 30 is relatively incompressible, thediaphragms magnetic fluid 30 is increased and the conductance of the capillary 15 is decreased. Damping also can be used to limit the high frequency response of the transducer. - As illustrated in Fig. 3 in another implementation of the invention, a further increase in sensitivity is achieved by affixing an
element 28 made of a solid, magnetically soft material, such as iron, to the center of thediaphragm 13. Theelement 28 is disposed within the magnetic fluid inchamber 24 and has a higher saturation magnetization than the magnetic fluid. Theelement 28 also can provide stiffness to the central portion of the diaphragm. To preserve shock insensitivity, anelement 29 is located in thechamber 16 and is affixed to thediaphragm 17. Theelement 29 may be substantially identical to theelement 28,or may be of a nonmagnetic material with suitable size and shape to achieve the desired insensitivity. - Fig. 5 is a curve representing the changes in pressure (psi) as a function of current (milliamps). In an actual implementation of the invention, a 450 Gauss, 400 cp Ferrofluid was used. The
element 28 is a steel slug of 3/8-inch (9,52 mm) diameter and 3/16-inch (4,76 mm) long cemented to thediaphragm 13 with RTV silicone sealant. The air supply pressure is 18 psi (1,22 atm). It should be understood that these parameters, materials and dimensions are exemplary and the invention is not limited thereby. - In an alternative approach the transducer comprises a single chamber and a single flexible diaphragm. In such case an air space is provided above the level of the magnetic fluid to allow displacement of the diaphragm.
- In another approach,
nozzle 10 is made of magnetic material and functions also aspole piece 11. In this approach, the outercoaxial member 11 and holes 12 shown in Figure 4 are eliminated. - The novel current-to-pressure transducer disclosed herein employs a magnetic fluid to coact with flexible diaphragms disposed in close juxtaposition to a nozzle of an air line. The transducer lends itself to mass production and low cost, is efficient in operation, and does not require individual adjustments.
- Another feature of this invention is a nozzle and pole piece structure that is formed from a
rod 40 made of a magnetic material, such as Carpenter High Permeability "49" Alloy, for example. Therod 40 has a diameter of about 3/16 inch (4,76 mm) in this particular embodiment. As illustrated in Fig. 6, themagnetic rod 40 is formed withfunctional pole pieces 41 at a slotted end of therod 40.Slots 43 allow the escape of excess air and are relatively easy to machine, with saw blades or slot cutters, as compared to the formation of individual bleed holes 12 and the associated deep circumferential groove betweenelements pole pieces 41 provide magnetic flux for coaction with electric current flowing through the electrical coil (not shown) of the electromagnetic circuit. Application of electric current to the coil causes themagnetic fluid 30 to move which, in turn, causes the deformation of the flexible diaphragm as explained heretofore thereby controlling air flow through the nozzle . - The
rod 40 has a threadedpart 42 for engagement with a threadedcap 44 of a housing assembly, shown in Fig. 9. Therod 40 also has ahexagonal part 47 formed at the end adjacent to the threadedpart 42 to allow the rod to be turned so that the height of the nozzle relative to the diaphragm can be adjusted for proper operation, and locked withnut 68. - Figure 7 shows an end view of the nozzle and
pole piece structure 40 viewed from the slotted end. Therod 40 is formed with one or more of thelongitudinal slots 43, which extend inwardly to at least the outer diameter of a relativelyshallow groove 46 formed within the end of therod 40. Theslots 43 serve the same purpose as theholes 12 depicted in Fig. 2 to allow the escape of excess air, but are easier to machine and fabricate than the transverse holes.Groove 46 may be eliminated if theslots 43 extend inward to the proximity of the constrictedpassage 49. - As depicted in Figs. 8A and 8B, an open channel is formed within the interior of the
nozzle tube 48 to allow the passage and escape of air. Thenozzle tube 48 may be tapered at the end portion that faces the diaphragm so that aconstricted passage 49 is formed at the end of thenozzle channel 48. Theconstricted portion 49 of the channel 48 (Figs. 8A and 8B) reduces the volume of air that escapes from the nozzle at a given pressure. The amount of air flow from thechannel portion 49 is regulated by the position of thediaphragm 13, which is controlled by the action of the magnetic fluid in response to the electric current supply to the coil of the electromagnetic circuit. - The exploded view of Fig. 9 shows the
main housing 50 for the integral nozzle and pole piece structure which is made of soft iron. Diaphragms 52 and 54 are spaced by asoft iron spacer 56 formed withmagnetic fluid chambers aluminum retainer 66 is located adjacent to thediaphragm 54 for connection to thespacer 56. Alock nut 67 is located against theretainer 66 and fourcap screws 70 tie thespacer 56 andretainer 66 with thediaphragms main housing 50. A second nozzle (not shown) may be threaded intoretainer 66 to coact withdiaphragm 54. - At the other end of the
housing 50, the threadedelement 44, which is made as a soft iron cap with internal threads for engaging the nozzle, is joined with alock nut 68 by means of four Allensocket cap screws 72 to themain housing 50. - Fig. 10 depicts the assembled unit which has a
notch 74 in thehousing 50 to allow connection of electrical circuitry to the electrical coil of the electromagnetic circuit and to permit escape of excess air. - By virtue of the integral structure of a nozzle and pole piece which are machined from a single magnetic rod, the end of the
nozzle tube 46 and the end of thepole piece 41 are substantially coplanar. When the electromagnetic force is applied to the top surface of thediaphragm 13 by themagnetic fluid 30, the lower surface of the diaphragm conforms to the shape of thepole piece 41. Since the alignment of the ends of thepole piece 41 andnozzle tube 46 are in substantial planar alignment, the diaphragm will provide a complete seal at the face of the nozzle. With the nozzle and pole piece structure design as disclosed herein, any canting of thediaphragm 13 is self-corrected because the force on the diaphragm acts between a point of first contact of thediaphragm 13 with the end of the largerdiameter pole piece 41 and the coplanar end of the nozzle tube. The integral nozzle and pole piece structure also is easier to fabricate with theslots 44 formed at the end of the rod structure to allow the desired air escape instead of with transverse holes as used in prior nozzle assemblies. Such transverse holes either require a difficult process to machine a deep groove between thenozzle 10 andpole piece 11, or require fabricating thenozzle 10 andpole piece 11 separately, in which case it would be difficult to assemble these parts to achieve the desired coplanarity.
Claims (16)
- A current-to-pressure transducer comprising:- a baseplate (19) or housing made of magnetic material;- at least one chamber (14) formed in said baseplate (19), said chamber having an open end being sealed by a flexible membrane or diaphragm (13);- air supply means (24) having an exhaust nozzle (10) disposed closely adjacent to said flexible diaphragm (13);- electromagnetic means including a coil (23) wound around a magnetic core member (22, 31) which is provided at one end with a magnetic pole piece (11) disposed closely adjacent to said flexible diaphragm (13), the other end of said magnetic core member (22, 31) being joined to said baseplate (19) in a magnetically conductive manner; and- a source of input current (27, 34) connected to said coil (23) to provide a magnetic field in the gap between said pole piece (11) and said diaphragm (13) for displacing said flexible diaphragm (13) relative to said nozzle (10) thereby varying the air pressure in said air supply means (24) in accordance with said input current;characterised by a volume of magnetic fluid (30) contained within said chamber (14), with said magnetic field acting within at least a portion of the volume of said magnetic fluid (30), wherein the displacement of said flexible diaphragm (13) is accomplished with the volume of said magnetic fluid (30) conserved and maintained constant, whereby the volume of magnetic fluid (30) that is displaced in said chamber (14) associated with the displacement of said flexible diaphragm (13) is compensated by accumulator means (16, 17) arranged in said baseplate (19).
- A current-to-pressure transducer as in claim 1, wherein said core member comprises a magnetic tubular element (22) and said coil (23) is wound about said element.
- A current-to-pressured transducer as in claim 2, wherein said air supply means comprises a tube (24) disposed coaxially within said magnetic tubular element (22).
- A current-to-pressure transducer as in one of the preceding claims, including a magnetic piece (28) positioned within said chamber (14) adjacent to said diaphragm (13).
- A current-to-pressure transducer as in one of the preceding claims, wherein an air space is provided within said chamber (14) to allow displacement of said diaphragm.
- A current-to-pressure transducer as in one of the preceeding claims, including a pressure sensing means (26) and an electronic feedback circuit (27) for limiting the current to said coil (23) so that the pressure is substantially linearly related to the input current.
- A current-to-pressure transducer as in one of the preceeding claims, including means (25) for maintaining said membrane or diaphragm (13) in position at said open end of said chamber (14).
- A current-to-pressure transducer according to claim 1, comprising a second chamber (16) and a means (15) connecting said first and second chambers (14, 16), said second chamber (16) having an open end being sealed by a second flexible membrane or diaphragm (17) for containing said magnetic fluid (30) within said chambers (14, 16) and said connection means (15), with said electromagnetic means (23, 22, 31) when energized coacting with said magnetic fluid (30) to deform a selected one of said diaphragms (13, 17).
- A current-to-pressure transducer as in claim 8, wherein said electromagnetic means (23, 31) is positioned for coacting with said magnetic fluid (30) in one (14) of said chambers (14, 16) to deform a selected one (13) of said diaphragms (13, 17), and said air supply means (24) is positioned for coacting with the other one (17) of said diaphragms (13, 17).
- A current-to-pressure transducer as in claim 8 or 9, wherein the diaphragms (13, 17) are coplaner.
- An integral nozzle and pole piece structure for use with a current-to-pressure transducer according to any of the preceding claims, said structure comprising:- a longitudinal rod (40) made of magnetic material;- a nozzle tube (48) formed in a central portion of said rod (40) for allowing the passage of air received from an air supply;- one end of said rod (40) forming a magnetic pole piece (41), said pole piece end being substantially coplanar with an end of said nozzle tube (48);- longitudinal slots (43) formed at said one end of said rod (40) for allowing the escape of air.
- A structure as in claim 11, including a groove (46) encompassing said nozzle tube (48), said slots (43) being connected to said groove (46).
- A structure as in claim 11 or 12, including a threaded element (42) seated on a portion of said rod (40) adjacent to the other end of said rod (40), a housing cap (47) for engaging said threaded element (42), and means formed integral with said rod (40) for rotating said rod (40) and said threaded element (42) for adjusting the position of said nozzle tube (48).
- A structure as in one of the claims 11 to 13, wherein said nozzle tube (48) is tapered at one end to form a constricted portion (49) for changing the pressure of said air flow.
- A structure as in one of the claims 11 to 14, including a housing (50) for containing said longitudinal rod (40) comprising said nozzle (49) and pole piece (41).
- A structure as in claim 15, including an opening (74) formed in said housing (50) for allowing access of electrical circuit connection and for permitting escape of excess air.
Applications Claiming Priority (4)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US281125 | 1988-12-07 | ||
US07/281,125 US4874005A (en) | 1988-12-07 | 1988-12-07 | Current to pressure tranducer employing magnetic fluid |
US414395 | 1989-09-29 | ||
US07/414,395 US4984600A (en) | 1989-09-29 | 1989-09-29 | Self correcting nozzle useful with current to pressure transducer |
Publications (2)
Publication Number | Publication Date |
---|---|
EP0380762A1 EP0380762A1 (en) | 1990-08-08 |
EP0380762B1 true EP0380762B1 (en) | 1994-01-19 |
Family
ID=26960725
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP19890119767 Expired - Lifetime EP0380762B1 (en) | 1988-12-07 | 1989-10-24 | Current to pressure transducer employing magnetic fluid with self-correcting nozzle |
Country Status (5)
Country | Link |
---|---|
EP (1) | EP0380762B1 (en) |
JP (1) | JP2539931B2 (en) |
AU (1) | AU619927B2 (en) |
CA (1) | CA1336784C (en) |
DE (1) | DE68912562T2 (en) |
Family Cites Families (11)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US2939673A (en) * | 1953-12-23 | 1960-06-07 | Honeywell Regulator Co | Electromechanical elements |
US2869818A (en) * | 1958-01-03 | 1959-01-20 | Fleuret Marcel | Electromagnetic metering valve |
US3272078A (en) * | 1964-10-12 | 1966-09-13 | Honeywell Inc | Controlling apparatus |
GB1140785A (en) * | 1966-07-29 | 1969-01-22 | Sperry Rand Corp | Improvements relating to control systems |
DE1600840A1 (en) * | 1967-02-06 | 1970-02-05 | Licentia Gmbh | Control valve |
US3426970A (en) * | 1968-03-25 | 1969-02-11 | Honeywell Inc | Vibration damping nozzle and flapper |
US3817488A (en) * | 1971-10-04 | 1974-06-18 | Northeast Fluidics Inc | Electro-pneumatic device |
US4053952A (en) | 1975-10-10 | 1977-10-18 | The United States Of America As Represented By The Secretary Of The Department Of Health, Education And Welfare | Magnetic fluid actuated control valve, relief valve and pump |
US4579137A (en) | 1981-10-06 | 1986-04-01 | Inotek, Inc. | Electro-pneumatic current to pressure transducer and pneumatic and electronic control circuits therefor |
GB2181818B (en) * | 1985-10-18 | 1989-10-25 | Ti Domestic Appliances Ltd | Fluid flow control valve |
JP2621321B2 (en) * | 1988-03-31 | 1997-06-18 | 株式会社島津製作所 | Fluid pressure regulating valve device |
-
1989
- 1989-09-29 CA CA 614828 patent/CA1336784C/en not_active Expired - Fee Related
- 1989-10-24 DE DE1989612562 patent/DE68912562T2/en not_active Expired - Fee Related
- 1989-10-24 EP EP19890119767 patent/EP0380762B1/en not_active Expired - Lifetime
- 1989-12-01 JP JP1314132A patent/JP2539931B2/en not_active Expired - Lifetime
- 1989-12-06 AU AU45985/89A patent/AU619927B2/en not_active Ceased
Also Published As
Publication number | Publication date |
---|---|
DE68912562T2 (en) | 1994-05-05 |
JPH02225803A (en) | 1990-09-07 |
CA1336784C (en) | 1995-08-22 |
AU4598589A (en) | 1990-06-14 |
JP2539931B2 (en) | 1996-10-02 |
DE68912562D1 (en) | 1994-03-03 |
EP0380762A1 (en) | 1990-08-08 |
AU619927B2 (en) | 1992-02-06 |
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