WO1998017974A1 - Capteur de position a couplage magnetique - Google Patents

Capteur de position a couplage magnetique Download PDF

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Publication number
WO1998017974A1
WO1998017974A1 PCT/US1997/019025 US9719025W WO9817974A1 WO 1998017974 A1 WO1998017974 A1 WO 1998017974A1 US 9719025 W US9719025 W US 9719025W WO 9817974 A1 WO9817974 A1 WO 9817974A1
Authority
WO
WIPO (PCT)
Prior art keywords
actuator
assembly
magnets
slide
recited
Prior art date
Application number
PCT/US1997/019025
Other languages
English (en)
Inventor
Lewis W. Tedstone
Robert V. Murphy
Original Assignee
Data Instruments, Inc.
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Data Instruments, Inc. filed Critical Data Instruments, Inc.
Publication of WO1998017974A1 publication Critical patent/WO1998017974A1/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
    • G01D5/02—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using mechanical means
    • G01D5/06—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using mechanical means acting through a wall or enclosure, e.g. by bellows, by magnetic coupling
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F23/00—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm
    • G01F23/30—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by floats
    • G01F23/64—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by floats of the free float type without mechanical transmission elements
    • G01F23/68—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by floats of the free float type without mechanical transmission elements using electrically actuated indicating means
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F23/00—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm
    • G01F23/30—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by floats
    • G01F23/64—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by floats of the free float type without mechanical transmission elements
    • G01F23/72—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by floats of the free float type without mechanical transmission elements using magnetically actuated indicating means

Definitions

  • This invention relates to a position sensor for sensing a position between at least two points.
  • a potentiometer within the position sensor is magnetically coupled to an element whose position is being monitored.
  • a position of an apparatus or moving member within a harsh or corrosive environment. This could be either a liquid or gaseous environment or one where abrasive contaminants, such as small metal shavings, are present.
  • a level of a liquid in a tank or container is measured by detecting a position of a float.
  • the position of a striking arm in a stamping press is monitored.
  • the liquid level or arm position must be measured precisely since an inaccurate measurement may compromise the process results.
  • any device for measuring the liquid level must be sealed so as to be able to withstand the harsh environmental conditions. Linear position detectors are commonly available. For example, Data Instruments, Inc.,
  • a linear position transducer 10 includes a housing 12 and an output cable 14 for providing a signal representative of linear position.
  • a shaft 16 is attached at one end to a component 18 whose linear position is being measured.
  • the component 18 moves back and forth in a direction represented by the double-headed arrow A, thus causing the shaft 16 to move in and out of the housing 12.
  • the shaft 16 must be at least as long as the range of measured linear motion of the component 18.
  • the overall space required for the linear position detector 10 would be, therefore, almost twice the length of movement to be measured.
  • the known linear position detector 10 requires that the shaft 16 be exposed to the environment within which the component 18 is operating. As above, this environment can include corrosive liquids which must not be allowed to penetrate inside the housing 12. Accordingly, precautions must be taken to seal the opening through which the shaft 16 enters the housing 12. As the shaft 16 is moving in and out of the housing 12, it is oftentimes difficult to completely seal the inside of the housing 12 from the outside environment. It is especially important that the shaft be sealed when the linear position detector is used to detect linear position within a corrosive liquid or gas environment.
  • a liquid level sensor system includes a float assembly for placement into the liquid.
  • the float assembly is buoyant relative to the liquid, and is placed around a circular sealed tube set perpendicular to the liquid's surface.
  • Three pairs of wheels allow the float assembly to move along an outer surface of the tube. The wheels are oriented to roll only in a direction along the tube.
  • three U-shaped magnets are symmetrically placed around the circumference of the float assembly. Each U-shaped magnet is positioned so that its two poles face the surface of the tube.
  • a movable carriage is positioned within the tube. The carriage moves inside the tube and includes a system of wheels mounted thereon. These wheels allow the carriage to move only in the direction along the tube.
  • U-shaped magnets are positioned on the carriage to magnetically couple, respectively, with the U-shaped magnets on the float assembly. Therefore, when magnetically coupled together, movement of the float assembly will cause the carriage system to move.
  • An optical reflector is mounted on the carriage.
  • An optical light source provides a semi-coherent beam of light through an optical fiber at the top of the tube. The light passes along a center-line of the tube and is reflected by the reflector back into the fiber. The portion of the optical path between the end of the fiber and the reflector varies with the position of the float.
  • a photodetector receives light reflected from the reflector and provides an output to a frequency counter.
  • the Fling system oscillates at a fundamental frequency that is inversely proportional to the round trip path of the light including electrical path delay time.
  • the only variable in the system is the distance between the end of the optical fiber and the reflector on the carriage. Thus, the oscillation frequency is a function of that variable distance and, therefore, related to the level of the liquid.
  • the Fling patent describes a linear position detector which is used to measure a liquid level which does not use a shaft moving in and out of the central tube.
  • a linear position detector which is used to measure a liquid level which does not use a shaft moving in and out of the central tube.
  • potential contamination of the inside of the tube is reduced since the cable carrying the light beam does not physically move during operation and it is then easier to seal the opening against leaking.
  • the linear position detector of Fling need only be slightly longer than the range of motion to be measured since a moving shaft is not utilized.
  • the liquid level sensor as described by Fling appears to be a complex device including an optical source which includes a microprocessor, a frequency counter, a detector, an LED and an optical fiber. Further, it appears that the lens and reflector within the tube would have to be of high optical quality so as not to introduce errors into the accuracy of the measurement. As a result, the liquid level sensor of Fling is complex and would appear to be more expensive, due to the parts being used, than other commercially available sensors.
  • Fling also relies on guide wheels to facilitate movement of the float assembly along the outside of the tube as well as for easing movement of the reflector carriage within the tube.
  • These wheels notably the wheels on the float assembly, may be susceptible to being jammed or becoming stuck due to exposure to the liquid or environment in which the sensor is placed.
  • an accurate position sensor is needed which is simple to build, compact, inexpensive, not susceptible to damage due to placement in harsh environments and which maintains magnetic coupling during operation.
  • the present invention provides a position sensor with magnetic coupling which accurately measures position without complex control circuitry and which is less susceptible to magnetic decoupling.
  • An actuator assembly is disposed around a central housing and magnetically coupled to a slide assembly within the housing.
  • the interior slide assembly is in operative contact with a linear potentiometer to provide a voltage signal proportional to a position of the interior slide assembly which follows the actuator assembly and, therefore, represents the position.
  • Magnets are provided in both the actuator and slide assemblies so as to couple the actuator and slide assemblies together with low hysteresis thus providing increased repeatability characteristics.
  • a position sensor in one embodiment, includes a housing having an outer surface of a longitudinal length, and an inner chamber; an actuator assembly disposed so as to move along the longitudinal length of the housing between a first point and a second point on the outer surface; and a slide assembly disposed within the inner chamber of the housing and magnetically coupled to the actuator assembly so as to move within the inner chamber as the actuator assembly moves along the outer surface of the housing, the slide assembly to output a voltage level proportional to a distance between the actuator assembly and the first point.
  • the position sensor includes a first actuator magnetic assembly disposed within the actuator assembly; and a slide magnetic assembly disposed within the slide assembly and magnetically coupled to the first actuator magnetic assembly.
  • an apparatus for magnetically coupling a first assembly to a second assembly which comprises a first pair of magnets, each magnet having a first portion of a first polarity and a second portion of a second polarity, disposed in the first assembly, with the first portions having the first polarity of each magnet positioned opposite one another; and a second pair of magnets, each magnet having a first portion of the first polarity and a second portion of the second polarity, disposed in the second assembly, with the second portion having the second polarity of each magnet positioned opposite one another, the second pair of magnets disposed parallel to the first pair of magnets so as to magnetically couple therewith.
  • Fig. 1 is a representation of a known linear position detector
  • Fig. 2A is an overview of an application of a position sensor for measuring a level of a liquid
  • Fig. 2B is an alternate configuration of a position sensor for measuring a liquid level
  • Fig. 3 A is a representation of a position sensor according to the present invention.
  • Fig. 3B is an alternate embodiment of a position sensor according to the present invention.
  • Fig. 4 is side view and end-view of a magnet used in the present invention
  • Fig. 5 A is a detailed view of a potentiometer used within the position sensor of the present invention
  • Fig. 5B is an electrical schematic describing operation of the potentiometer of Fig. 5 A;
  • Fig. 6 is a cross-sectional view of the position sensor as shown in Fig. 3 A;
  • Fig. 7 is a block diagram of an analog-to-digital converter for use in the position sensor;
  • Fig. 8 is an alternate embodiment of magnet shapes used in the present invention;
  • Figs. 9 and 9B are alternate embodiments of locations of magnets used in the present invention.
  • a position sensor 100 adapted to measure a level of a liquid is shown in Fig. 2 A.
  • the position sensor 100 includes a central housing 102 and an actuator assembly 104 disposed around the central housing 102.
  • a cable assembly 106 provides an output of the position sensor 100.
  • the actuator assembly 104 is manufactured so as to float within the liquid. In other words, the actuator assembly 104 has a density which is less than the liquid's density.
  • the position sensor 100 is then mounted via mounting supports 112 or other means to a sidewall 114 of the tank 110.
  • the position sensor 100 is mounted such that the central housing 102 is perpendicular to the surface of the liquid in the tank 110. It is, however, possible to mount the position sensor 100 other than perpendicular to the liquid's surface.
  • the position sensor 100 can be mounted in a cover 111 to be disposed over the tank 110.
  • the central housing 102 includes a portion 103, which is adapted to be screwed into the cover 111.
  • the position sensor 100 would be positioned in the liquid and the actuator assembly 104 would then float in the liquid so as to measure the liquid level 108.
  • the actuator assembly 104 moves along an outer surface of the central housing 102.
  • a length of the central housing 102 is chosen so that the range of measurement of the position sensor 100 is sufficient to measure a desired range of the liquid level 108.
  • the actuator assembly 104 is disposed around the central housing 102.
  • the central housing 102 has a circular cross-section, in other words, the central housing 102 is, effectively, a cylinder.
  • the actuator assembly 104 has an opening in its center through which the central housing 102 is positioned.
  • the actuator assembly 104 and the central housing 102 are coaxial.
  • the central housing 102 could also have a cross-section which is other than circular and the actuator assembly 104 would necessarily have a central opening which corresponds to the cross-section of the central housing 102.
  • a cylindrical central housing is shown, the housing could also have other shapes, for example, but not limited to, triangular, rectangular or square.
  • This configuration provides excellent coupling characteristics in that, once the magnetic coupling is established, only under the most extraordinary circumstances, i.e., when magnetic decoupling is the goal, will the coupling between the actuator and slide assemblies be removed.
  • a novel orientation of magnetic fields in each of the actuator and slide assemblies is provided. Magnetic fields in the actuator assembly are established with opposite polarities respectively to magnetic fields in the slide assembly. A magnetic line loop is created and the strong magnetic attraction between these opposite polarity fields couples movement of the actuator assembly to the slide assembly.
  • the actuator assembly 104 includes two actuator magnets 200, 202.
  • Each actuator magnet 200, 202 has first and second portions, or ends, magnetized, respectively, as north and south poles. As shown in Fig. 4, each actuator magnet 200, 202 has a length L and is magnetized parallel to its length. Further, the actuator magnets 200, 202 may have any cross-section, for example, be either circular, triangular or rectangular. In a preferred embodiment, the magnets have a circular cross-section with a diameter 0.
  • the actuator magnets 200, 202 are positioned within the actuator assembly 104 in series, i.e., substantially coaxial, with one another and parallel to the length of the central housing 102.
  • a spacer 201 is positioned between the actuator magnets 200, 202.
  • the spacer 201 is made from a non-magnetically coupling material, e.g., a plastic such as Delrin® available from DuPont.
  • the central housing 102 includes an inner chamber 204 in which a slide assembly 206 is positioned.
  • the slide assembly 206 includes two slide magnets 208, 210 which can be constructed similarly to the actuator magnets 200, 202. It is not necessary, however, that the actuator magnets have the same cross-section or length as the slide magnets. In a preferred embodiment, the slide magnets are, however, also circular in cross-section.
  • Each slide magnet 208, 210 has a length L and has two portions or ends, i.e., a north pole and a south pole.
  • the slide magnets 208, 210 are also positioned in series, i.e., substantially coaxial with one another, and parallel to the length of the central housing 102.
  • a spacer 209 is placed between the slide magnets 208, 210.
  • the south poles of the slide magnets 208, 210 are positioned in opposition to one another within the slide assembly 206.
  • the north poles of the slide magnets 208, 210 would be positioned in opposition to one another within the slide assembly 206.
  • the slide magnets 208, 210 within the slide assembly 206 are magnetically coupled with the actuator magnets 200, 202 within the actuator assembly 104.
  • the slide assembly 206 will correspondingly move within the inner chamber 204 of the central housing 102.
  • the actuator magnets and slide magnets are magnetically coupled to one another it is very difficult, under most operating conditions, to decouple them.
  • all the couplings need to be overcome in order to decouple the two assemblies.
  • the arrangement of the actuator magnets 200, 202 relative to the slide magnets 208, 210 minimizes the effects of hysteresis as between movement of the actuator assembly 104 and the slide assembly 206. In other words, movement of the actuator assembly 104 results in almost immediate movement of the slide assembly 206. Further, this arrangement of the actuator and slide magnets optimizes the repeatability characteristics of the device.
  • the size is a factor in determining the necessary sizes of the slide and actuator magnets as well as their respective magnetic strengths. These magnetic requirements may be met by different magnetic materials. As an exemplary, but non-limiting example, a position sensor with a central housing 102 having a cross- section with a diameter of approximately 3/8 inches will be discussed.
  • the "air-gap" which is found between the actuator assembly 104 and the slide assembly 206 is one factor which determines the size and strength of the magnets required in order to provide sufficiently strong magnetic coupling between the two assemblies.
  • rare earth Samarium Cobalt (SmCo) magnets with a length L of .125 inches and a diameter 0 of .250 inches having a Maximum Energy Product (BHmax) in the range of 20-30 Mega Gauss Oersteds (MGOe) are used for the actuator magnets 200, 202.
  • a Samarium Cobalt magnet with a length L of .125 inches and a diameter 0 of .125 inches and having a maximum energy product in the range of 20-30 MGOe are chosen for the slide magnets 208, 210. In this embodiment, these magnets will provide sufficient magnetic coupling between the two assemblies.
  • First and second actuator magnets 250, 252 are each magnetized parallel to their length L and include an ink mark 254 indicating the south pole of each magnet.
  • First and second actuator magnets 250-1, 252-1 are oriented with their respective south poles facing in a same first direction.
  • the second pair of first and second actuator magnets 250-2, 252-2 are oriented with their respective south poles facing in a same second direction different from the first direction.
  • a spacer 201 is provided between the two pairs of first and second actuator magnets.
  • Slide magnets 260 are also magnetized parallel to their length L and include the ink mark 254 indicating the south pole.
  • a first group of slide magnets 260-1, 260-2, 260-3 are positioned with their south poles oriented in the same direction, in this case, the second direction.
  • a second group of slide magnets 260-4, 260-5, 260-6 are oriented with their south poles facing in the same direction, in this case the first direction.
  • a spacer 209 is provided between the two groups of slide magnets.
  • the first group of slide magnets 260-1, 260-2, 260-3 magnetically couple with the first pair of actuator magnets 250-1, 252-1.
  • the second group of slide magnets 260-4, 260-5, 260-6 magnetically couple with the second pair of actuator magnets 250-2, 252-2.
  • the magnets combine to create magnetic fields in the actuator and slide assemblies which couple to one another. Any number of magnets of various sizes and strengths could be used. In an exemplary, but non-limiting example, the particular magnets needed for a central housing having a circular cross-section of approximately 1/2 of an inch will be described. Due to the slightly larger air-gap of this example, Neodymium-Iron-Boron (Nd-Fe-B) magnets are chosen. Each of the first external magnets 250 has a length L of .250 inches and a diameter 0 of .250 inches with a maximum energy product in a range of 30-40 MGOe.
  • Nd-Fe-B Neodymium-Iron-Boron
  • the second external magnet 252 has a length L of .125 inches with a diameter 0 of .250 inches and a maximum energy product in a range of 30-42 MGOe.
  • Each of the slide magnets 260 has a length L of .125 inches with a diameter 0 of .125 inches and have a maximum energy product in the range of 30-39 MGOe.
  • a linear potentiometer 212 is provided within the inner chamber 204 of the central housing 102 and extends along the length of the central housing 102.
  • the linear potentiometer 212 is made from a conductive plastic strip with a terminal at each end and includes a surface which has an electrical resistance which is proportional to its length. Effectively, the plastic strip is a resistor which can be "tapped” at any point on its surface. The longer the distance between any two tap points, the higher the resistance.
  • a voltage potential defined as a difference between a voltage at one end and a voltage at the other end of the potentiometer, is provided across the linear potentiometer 212. Thus, a voltage measured at a point along the surface of the linear potentiometer 212 will have a value somewhere between the voltage at one end of the linear potentiometer 212 and the voltage at the other end.
  • a linear conductive collector strip 214 has a same length as the linear potentiometer 212 and is provided within the inner chamber 204 in parallel with the linear potentiometer 212.
  • the linear conductive collector 214 is also made from a conductive plastic material but has effectively no, or minimal, electrical resistance across its surface.
  • both the linear potentiometer 212 and the linear conductive collector 214 are made of MystR® conductive plastic film available from Data Instruments, Inc. of Acton, Massachusetts.
  • the linear potentiometer 212 is doped to have the appropriate resistance characteristics. Of course, any material having appropriate conductivity characteristics can be used.
  • a wiper assembly 216 is attached to the slide assembly 206.
  • the wiper assembly 216 in a preferred embodiment, includes two wiper blades which are biased so as to, respectively, contact the surface of the linear potentiometer 212 and the surface of the linear conductive collector 214.
  • the wiper blades in a preferred embodiment, are made from one or more precious metals so as to increase electrical conductivity. For example, Platinum, Palladium, silver and gold can be combined in different amounts to create alloys for different functional requirements. In addition, depending upon the application, the components of the alloy may differ.
  • a potential at a point where the one wiper blade contacts the surface of the linear potentiometer 212 is electrically coupled to the linear conductive collector 214. Since the wiper assembly 216 is connected to the slide assembly 206, which is magnetically coupled to the actuator assembly 104, as the actuator assembly 104 moves in response to the liquid level 108, a voltage will appear on the linear conductive collector 214 which is a function of the liquid level 108.
  • the physical and electrical characteristics of the wiper assembly 216, the linear potentiometer 212 and the linear conductive collector 214 will be described in more detail with reference to Figs. 5A and 5B. As can be seen, the linear potentiometer 212 and linear conductive collector 214 are positioned substantially parallel to one another. Of course, one of ordinary skill can see that other orientations are possible.
  • the linear potentiometer 212 includes a first terminal 300 and a second terminal 302.
  • the linear conductive collector 214 also includes a terminal 304.
  • a ground potential is provided at the first terminal 300 and a voltage of +10 volts is provided at the second terminal 302.
  • a voltage appearing on the linear conductive collector 214 would be approximately +5 volts.
  • the voltage appearing on the linear conductive collector 214 should increase from +5 volts toward +10 volts.
  • the voltage appearing on the linear conductive collector 214 should decrease from +5 volts toward zero volts, i.e., ground.
  • the operation of the linear potentiometer 212 can be explained when it is considered to be a potentiometer 400 having a voltage V E across its terminals 300, 302, as shown in Fig. 5B.
  • the wiper assembly 216 then detects a voltage V e at a point between the two terminals 300, 302.
  • the liquid level 108 is associated with a point on the linear potentiometer 212 and its associated voltage level.
  • the slide assembly 206 will place the wiper assembly 216 at various points on the linear potentiometer 212.
  • the voltage appearing on the linear conductive collector 214 is then representative of the liquid level 108.
  • the first terminal 300 and the second terminal 302 are at, respectively, ground and +10 volts. It is clear that the position sensor 100 can be provided with a bi-polar representation of the liquid level if, for example, -5 volts were placed on the first terminal 300 with the second terminal 302 at +5 volts. Thus, at a point midway between the first and second terminals one would expect to find zero volts. This point could be calibrated with the placement of the position sensor 100 such that the actuator assembly 104, when at the midway point, is at a location which represents a nominal liquid level 108. A location marker could be provided on the exterior of the central tube to aid in calibration.
  • the wiper assembly 216 may be positioned closer to the first terminal 300 and thus output a negative voltage. Conversely, when the liquid level 108 is greater then the nominal level, a positive voltage would then be output.
  • the cable assembly 106 includes three wires with one to provide the first potential to the first terminal 300 of the linear potentiometer 212, another to provide the second potential to the second terminal 302 of the linear potentiometer 212 and a third wire to connect to the terminal 304 on the linear conductive collector 214. In a bi-polar version, as discussed above, there would be an additional wire to provide the negative voltage.
  • the position sensor 100 can be modified to output a digital representation of the linear position in place of or in addition to, the analog voltage output.
  • an analog-to-digital converter (ADC) 700 can be provided within the inner chamber 204.
  • the ADC 700 is connected to the terminal 304 of the linear conductive collector 214 to receive the voltage V e at an input 702.
  • An output 704 of the ADC 700 would, for example, include eight bits of digital data (0:7) representing the input voltage V e . Of course, depending upon the resolution of the ADC 700, either more or less output bits could be provided.
  • the addition of the ADC 700 would provide the position sensor 100 with the ability to be located farther away from the monitoring system since the digital signal would not degrade over distance.
  • a sensing apparatus which receives the analog output V e is limited as to how far away from the position sensor 100 it can be located since voltage drop due to the length of the cable 106 may compromise the measurement accuracy.
  • three pairs of actuator magnets 200, 202 are disposed within the actuator assembly 104. As shown in Fig. 6, the three pairs of actuator magnets 200, 202 are symmetrically spaced around a circumference C of the actuator assembly 104 so as to be symmetrically spaced about the magnets in the slide assembly. In a preferred embodiment, with a circular central housing 102 and a circular actuator assembly 104, the three pairs of magnets are approximately 120° apart. Of course, the three pairs of magnets maybe evenly spaced even when the central housing is not circular.
  • the actuator magnets 200, 202 are positioned in series, i.e., substantially coaxial with one another.
  • the actuator magnets 200, 202 are arranged with the same orientation as shown and described in Fig. 3A, however, the actuator magnets 200, 202 are circumferentially offset from one another.
  • a first actuator magnet 200 is circumferentially offset from a second actuator magnet 202 along circumference C.
  • two actuator magnets 200, 202 are in separate planes along the longitudinal length of the central housing 102, they are not linearly in series, i.e., substantially coaxial with each other.
  • first actuator magnets 200, 200', 200" should be in a same plane and second actuator magnets 202, 202', 202" should be in an adjacent plane along the longitudinal length of the housing. Additionally, the spacing of the planes should be set appropriately so as to provide the magnetic coupling, as described above, between the slide magnets and the actuator magnets.
  • the actuator magnets were all at a same radial distance r, from the axis of the slide magnets.
  • the actuator magnets are not only offset from each other in that they are not substantially coaxial with each other, but also each actuator magnet of the pair of actuator magnets is at a different radial distance from the slide magnets. As shown in Fig.
  • the first actuator magnets 200, 200', 200" are at a distance r, from the center, i.e., an axis of the central housing, but the second actuator magnets 202, 202', 202" are at a second radius r 2 from the center and also offset circumferentially, i.e., along the circumference C, from their respective first actuator magnet 200, 200', 200".
  • the inner chamber 204 of the central housing 102 is sealed off from contamination by the environment in which the position sensor 100 is placed.
  • an end cap 600 closes the inner chamber 204.
  • An end cap seal 602 prevents contaminants from entering the inner chamber 204.
  • the end cap seal 602 in a preferred embodiment, includes an O-ring made from a suitable material, e.g., a copolymer, rubber or plastic.
  • a top cap 604 is provided at the other end of the central housing 102.
  • the cable assembly 106 is fed through an opening within the top cap 604.
  • a cable seal 606 prevents contaminants from entering around the cable assembly 106 while a top cap seal 608 prevents contaminants from entering the inner chamber 204 between the top cap 604 and the central housing 102.
  • the top cap seal 608 and the cable seal 606 can also each be an O-ring.
  • the central housing 102 is made a material of which resists the corrosive effects of most environments and through which a magnetic field can pass. Such materials include, for example, aluminum or plastic.
  • the outer surface of the central housing 102 may be anodized so as to facilitate smooth movement of the actuator assembly 104 along the surface. While the position sensor 100 has been described as having a central housing 102 having a circular cross-section, it is clear that the cross-section of the central housing could be other than circular. Specifically, triangular, rectangular or square cross-sections are meant to be within the scope of the present invention. With a triangular cross-section, three pairs of actuator magnets 200, 202 can still be symmetrically disposed around the slide assembly 206.
  • a fourth pair of actuator magnets 200, 202 can be disposed at 90° intervals in the actuator assembly 104 so as to symmetrically surround the slide assembly 206.
  • four pairs of actuator magnets 200, 202, spaced 90° apart could also be used with a central housing 102 having a circular cross-section.
  • An embodiment has been previously discussed where three pairs of actuator magnets are symmetrically disposed around the slide magnets.
  • two ring magnets 802, 804, as shown in Fig. 8, can be disposed in the actuator assembly. Each ring magnet 802, 804 would have a center opening 806 through which the central housing would fit.
  • the central opening 806 can be of any shape to accommodate the cross-sectional shape of the central housing.
  • the central housing has, for example, a triangular, rectangular or elliptical shape
  • the central opening 806 would have a corresponding shape.
  • the ring magnets 802, 804 would be positioned so that the like-polarized poles would be opposite each other. As shown in Fig. 8, the north poles are opposing each other.
  • the orientation of the ring magnets 802, 804 as shown in Fig. 8 would, therefore, operate with the orientation of the slide magnets as shown in Fig. 3A.
  • a spacer 808 would also be provided to maintain the spacing requirements of the magnets 802, 804.
  • the ring magnets 802, 804 could be almost any shape, for example, but not limited to, circular, square or triangular. Again, the central opening 806 would then be of any necessary shape to accommodate the central housing.
  • a first magnetic field having a south polarity is adjacent to a second magnetic field having a north polarity followed by a third magnetic field of south polarity.
  • a magnetic field intensity of the north polarized magnetic field between the two south polarized magnetic fields has a greater magnetic field intensity level than either of the two south polarity magnetic fields. This is due to the combination of the two north poles of the two magnets 802, 804.
  • the position sensor 100 was described above with a relatively straight central housing 102.
  • the linear potentiometer 212 in conjunction with the linear conductive collector 214 and the wiper assembly, provides the flexibility to have a central housing 102 which is curved so as to follow the movement of a component.
  • the radius of curvature of the central housing cannot be so sharp as to prevent movement of the actuator assembly 104 along the outer surface of the central housing.
  • the position sensor 100 was shown in an application to measure a liquid level, it is clear that the position sensor can be used in non-liquid level applications.
  • the actuator assembly 104 can be mechanically attached to any part which has a linear component of movement.
  • the position sensor 100 can be applied in an injection molding machine so as to monitor the position of a moving component of the machine.
  • the central housing 102 would be mounted in place and the actuator assembly would be mechanically attached to the moving component and held in a manner that maintains a uniform symmetrical distance between the actuator assembly and the central housing to avoid frictional contact between the central housing and the actuator assembly.
  • a position sensor has been described which accurately measures position.
  • the position sensor has a minimum of moving parts and is not susceptible to most vibration conditions.
  • the operation of the position sensor is protected from corrosive environments via the sealed central housing.
  • the configuration of the actuator and slide magnets creates a magnetic coupling which is not easily overcome.
  • the length of the central housing need only be a little bit longer than the linear displacement to be measured so as to provide for the end cap and mounting hardware.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Fluid Mechanics (AREA)
  • Transmission And Conversion Of Sensor Element Output (AREA)

Abstract

L'invention concerne un capteur de position comprenant un logement central et un ensemble actionneur placé de manière à se déplacer sur une longueur du logement central. Un ensemble glissière est prévu à l'intérieur du logement central, lequel est couplé magnétiquement à l'ensemble actionneur. Un potentiomètre linéaire est prévu à l'intérieur du logement central, et un ensemble frotteur fixé à l'ensemble glissière détecte une tension en un point situé le long du potentiomètre linéaire. La tension détectée le long du potentiomètre linéaire est directement liée à la position de l'ensemble glissière qui suit le mouvement de l'ensemble actionneur. Au moins deux aimants sont placés dans l'ensemble actionneur. Chaque aimant est doté d'une première et d'une seconde extrémités de polarités différentes. Ces deux aimants sont orientés de façon sensiblement coaxiale l'un par rapport à l'autre, de telle sorte que les extrémités respectives dotées d'une première polarité sont opposées l'une par rapport à l'autre. Deux aimants sont prévus à l'intérieur de l'ensemble glissière, chacun ayant deux extrémités de polarités différentes et étant disposés également de façon sensiblement coaxiale l'un par rapport à l'autre, les extrémités respectives de chacun, dotées d'une seconde polarité, étant placées en opposition l'une par rapport à l'autre, de manière à se coupler magnétiquement avec les aimants de l'ensemble actionneur.
PCT/US1997/019025 1996-10-18 1997-10-17 Capteur de position a couplage magnetique WO1998017974A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US2863496P 1996-10-18 1996-10-18
US60/028,634 1996-10-18

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WO1998017974A1 true WO1998017974A1 (fr) 1998-04-30

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Cited By (13)

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Publication number Priority date Publication date Assignee Title
EP1264991A1 (fr) * 2001-06-07 2002-12-11 Gefran Sensori S.r.l. Arrangement d'un détecteur de position dans une unité piston-cylindre
WO2003093682A1 (fr) * 2002-05-04 2003-11-13 Imi Vision Limited Ameliorations apportees a un appareil de controle de position
US20140066860A1 (en) * 2012-08-28 2014-03-06 Osprey Medical, Inc. Volume monitoring device
DE102012220412B3 (de) * 2012-11-28 2014-03-27 Seca Ag Längenmessgerät
DE102012220468B3 (de) * 2012-11-09 2014-03-27 Seca Ag Längenmessgerät
WO2018028147A1 (fr) * 2016-08-11 2018-02-15 东莞正扬电子机械有限公司 Procédé de détection de niveau de liquide et capteur de niveau de liquide
US9999718B2 (en) 2012-08-28 2018-06-19 Osprey Medical, Inc. Volume monitoring device utilizing light-based systems
WO2021091530A1 (fr) * 2019-11-05 2021-05-14 Halliburton Energy Services, Inc. Réduction de l'hystérésis magnétique d'un ensemble capteur de position
US11116892B2 (en) 2012-08-28 2021-09-14 Osprey Medical, Inc. Medium injection diversion and measurement
US11135375B2 (en) 2012-08-28 2021-10-05 Osprey Medical, Inc. Volume monitoring systems
US11248427B2 (en) 2018-08-06 2022-02-15 Schlumberger Technology Corporation Systems and methods for manipulating wellbore completion products
US11499841B2 (en) 2019-04-12 2022-11-15 Osprey Medical, Inc. Energy-efficient position determining with multiple sensors
WO2024039398A1 (fr) * 2022-08-15 2024-02-22 Halliburton Energy Services, Inc. Ensemble capteur de position à couplage magnétique circonférentiel pour opérations de puits de forage

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JPH07308060A (ja) * 1994-05-11 1995-11-21 Yaskawa Electric Corp 磁気カップリング装置

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DE2650294A1 (de) * 1976-11-02 1978-05-03 Gerhard Walter Prof Dr Seulen Magnetische kupplung fuer geraete zur niveau-, druck- oder stroemungsueberwachung fluessiger oder gasfoermiger medien
EP0039420A2 (fr) * 1980-04-28 1981-11-11 Bk Elektronik Messgeräte Gmbh Dispositif pour mesurer le niveau et la température moyenne de liquides en citernes
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US6745666B2 (en) 2001-06-07 2004-06-08 Gefran Sensori S.R.L. Position sensor for oil-operated piston/cylinder units
EP1264991A1 (fr) * 2001-06-07 2002-12-11 Gefran Sensori S.r.l. Arrangement d'un détecteur de position dans une unité piston-cylindre
WO2003093682A1 (fr) * 2002-05-04 2003-11-13 Imi Vision Limited Ameliorations apportees a un appareil de controle de position
US9999718B2 (en) 2012-08-28 2018-06-19 Osprey Medical, Inc. Volume monitoring device utilizing light-based systems
US20140066860A1 (en) * 2012-08-28 2014-03-06 Osprey Medical, Inc. Volume monitoring device
US11219719B2 (en) 2012-08-28 2022-01-11 Osprey Medical, Inc. Volume monitoring systems
US11135375B2 (en) 2012-08-28 2021-10-05 Osprey Medical, Inc. Volume monitoring systems
US11116892B2 (en) 2012-08-28 2021-09-14 Osprey Medical, Inc. Medium injection diversion and measurement
US10413677B2 (en) * 2012-08-28 2019-09-17 Osprey Medical, Inc. Volume monitoring device
WO2014072089A1 (fr) 2012-11-09 2014-05-15 Seca Ag Appareil de mesure de longueur
CN104755028A (zh) * 2012-11-09 2015-07-01 赛卡股份公司 长度测量装置
DE102012220468B3 (de) * 2012-11-09 2014-03-27 Seca Ag Längenmessgerät
US10143402B2 (en) 2012-11-09 2018-12-04 Seca Ag Length measuring device
JP2015535594A (ja) * 2012-11-09 2015-12-14 セカ アーゲー 長さ測定装置
US9579045B2 (en) 2012-11-28 2017-02-28 Seca Ag Length measuring device
DE102012220412B3 (de) * 2012-11-28 2014-03-27 Seca Ag Längenmessgerät
US10801875B2 (en) 2016-08-11 2020-10-13 Dongguan Zhengyang Electronic Mechanical Co., Ltd. Liquid level detection method and liquid level sensor
WO2018028147A1 (fr) * 2016-08-11 2018-02-15 东莞正扬电子机械有限公司 Procédé de détection de niveau de liquide et capteur de niveau de liquide
US11248427B2 (en) 2018-08-06 2022-02-15 Schlumberger Technology Corporation Systems and methods for manipulating wellbore completion products
US11499841B2 (en) 2019-04-12 2022-11-15 Osprey Medical, Inc. Energy-efficient position determining with multiple sensors
WO2021091530A1 (fr) * 2019-11-05 2021-05-14 Halliburton Energy Services, Inc. Réduction de l'hystérésis magnétique d'un ensemble capteur de position
GB2603384A (en) * 2019-11-05 2022-08-03 Halliburton Energy Services Inc Reducing magnetic hysteresis of a position sensor assembly
US11643903B2 (en) 2019-11-05 2023-05-09 Halliburton Energy Services, Inc. Reducing magnetic hysteresis of a position sensor assembly
GB2603384B (en) * 2019-11-05 2023-11-22 Halliburton Energy Services Inc Reducing magnetic hysteresis of a position sensor assembly
WO2024039398A1 (fr) * 2022-08-15 2024-02-22 Halliburton Energy Services, Inc. Ensemble capteur de position à couplage magnétique circonférentiel pour opérations de puits de forage

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