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
  • G01D5/12—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 electric or magnetic means
• • 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
  • F15B15/00—Fluid-actuated devices for displacing a member from one position to another; Gearing associated therewith
  • F15B15/20—Other details, e.g. assembly with regulating devices
  • F15B15/28—Means for indicating the position, e.g. end of stroke
  • F15B15/2815—Position sensing, i.e. means for continuous measurement of position, e.g. LVDT
  • F15B15/2861—Position sensing, i.e. means for continuous measurement of position, e.g. LVDT using magnetic means
• • 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
  • G01D11/00—Component parts of measuring arrangements not specially adapted for a specific variable
  • G01D11/24—Housings ; Casings for instruments
• • 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
  • G01D5/12—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 electric or magnetic means
  • G01D5/14—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 electric or magnetic means influencing the magnitude of a current or voltage
  • G01D5/142—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 electric or magnetic means influencing the magnitude of a current or voltage using Hall-effect devices
  • G01D5/145—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 electric or magnetic means influencing the magnitude of a current or voltage using Hall-effect devices influenced by the relative movement between the Hall device and magnetic fields
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
  • G01R33/00—Arrangements or instruments for measuring magnetic variables
  • G01R33/02—Measuring direction or magnitude of magnetic fields or magnetic flux
  • G01R33/025—Compensating stray fields

Definitions

• the present invention relates to a magnetic detector arrangement according to the preamble to claim 1. This magnetic detector arrangement allows for improved magnetic sensors .
• a switch or a sensor with a high resolution and which at the same time is insensitive to an external magnetic field it is desirable to position the magnet and the detector close to each other. In this way, it is possible to use a detector with a low sensitivity, obtaining a switch or a sensor that is more or less insensible to external magnetic fields.
• One problem with magnetic sensors is that the sensitivity of the detector must increase with an increased detection distance.
• a problem with the detector being very sensitive is that it will more easily be disturbed by an external, interfering magnetic field. This can e.g. occur when the sensor is close to a high current cable or a large transformer.
• a magnetic sensor can e.g. be built into a hydraulic cylinder in order to give the position of the piston head.
• a magnet is mounted to the piston head and a magnetic sensor detects the position of the magnet.
• This integrating of a magnetic detector in the cylinder leads to a greater distance between the magnet and the detector element, thus making the detector sensitive to external magnetic fields .
• the object of the invention is therefore to achieve an improved magnetic detector arrangement that is less sensitive to the influence of an outer magnetic field.
• the object of the invention is achieved in that the arrangement also comprises magnetic deflector means adapted for directing an external magnetic field in a direction parallel to the magnetic sensor element.
• a magnetic detector is obtained where the sensitivity to an outer magnetic field is reduced. This is achieved by using a magnetic deflector that direct the field lines of the outer magnetic field in a direction parallel to the magnetic sensor element. This allows for magnetic detector arrangements that have an improved resistance to a disturbing external magnetic field and/or an improved resolution.
• the magnetic means comprises two equally polarised magnets positioned at a predefined distance apart next to each other with the polarisation in the same direction. This improves the resolution and/or the resistance to external magnetic fields even further.
• the magnetic deflector means may be in the shape of one or more rods or a tube.
• the magnetic deflector means may be positioned in different positions.
• Fig. 1 shows a known hydraulic cylinder with a magnetic detector arrangement
• Fig. 2a shows an embodiment of the magnetic detector arrangement according to the invention
• Fig. 2b shows a side view of the embodiment in 2a
• Figs. 3a, 4a shows further embodiments of the magnetic detector arrangement according to the invention
• Figs. 3b, 4b shows a side view of the embodiment in
• Figs . 5, 6, 7 shows further embodiments of the magnetic detector arrangement according to the invention
• Fig. 8 shows a schematic view of a magnetic detector arrangement according to the invention.
• Fig 1 shows a known hydraulic cylinder 8 comprising a magnetic detector arrangement 1.
• the magnetic detector arrangement 1 consists of a magnetic element 4 and a magnetic sensor 2.
• the magnetic element 4 can comprise one or more magnets and is in this embodiment a circular ring magnet mounted to the piston head. In this way, the magnetic element will indicate the position of the piston head. The position is detected by the sensor which is mounted on the outside of the cylinder.
• the magnetic field of the magnetic arrangement will influence the softmagnetic core of the sensor and this influence can be detected by using the detector coil in a known manner. In this way, a contactless position detection is possible.
• the sensor can be analogue or with a number of discrete steps.
• the sensor preferably comprises a linear coil 9 and at least one softmagnetic core 10 that is to be saturated. Such a linear magnetic sensor is well known to the skilled person and is not described further.
• the circular magnets are used because the piston head is not fixed in a rotational direction inside the cylinder.
• a hydraulic cylinder where the rotation of the piston head is known or fixed, it is also possible to use a magnetic arrangement that does not cover the complete periphery of the piston head.
• the hydraulic cylinder is made of non-magnetic material, preferably stainless steel, but also other non-magnetic materials such as aluminium or a composite is possible, depending on e.g. the pressure in the cylinder.
• the piston rod is preferably made of hardened steel .
• the cylinder has inlets and outlets for the hydraulic oil. These are not shown in the figure.
• Such a hydraulic cylinder with a magnetic position detector is also well known to the skilled person.
• the hydraulic cylinder can e.g. be used for a steerable rear axle on a truck to indicate the position of the piston head and thus the steered wheel angle.
• a tubular extension is mounted to the hydraulic cylinder.
• This extension is made from a ferro-magnetic material, e.g. iron, and is mounted on the side of the cylinder along the longitudinal axis 12 of the cylinder.
• the extension tube can be either open at the end or be closed with a sealing to the rod.
• the purpose of this extension is to influence the magnetic field lines of the earth magnetic field in such a way that the magnetic field lines are forced to be more or less parallel to the magnetic sensor. In this way, the earth magnetic field will not influence the position detection of the piston head.
• the tubular extension is thus used as a magnetic deflector that directs the magnetic field lines in a direction parallel to the magnetic detector.
• the magnetic deflector functions in the following way.
• the magnetic field lines from a magnetic field are drawn to the magnetic deflector material since the magnetic deflector is made from a ferro-magnetic material. Consequently, some of the magnetic field lines from the magnetic field will be lead through the magnetic deflector and some field lines, with a distance to the magnetic deflector, will follow the same direction and thus will be parallel with the field lines passing through the magnetic deflector.
• By placing magnetic deflector means symmetrically in respect to the magnetic sensor will thus create a magnetic field that is substantially parallel to the magnetic sensor. This creates an area around the magnetic sensor with a magnetic field that is substantially homogenous and directed parallel with the sensor. Magnetic field lines passing in other directions through the magnetic sensor will thus be reduced significantly.
• the magnetic sensor is parallel to the travelling direction of the piston, i.e. the sensor extends in the same direction as the travelling of the piston.
• This longitudinal axis is denoted 12 in the figures. It is along this axis that the magnetic field lines of the external magnetic field are directed with the magnetic deflector. The centre of the tubular extension coincides with this axis 12.
• the magnetic detector arrangement comprises two magnetic deflectors 7 positioned parallel to the magnetic sensor and symmetric to a symmetry axis 11 running through the sensor element 2 and the magnet 4.
• the magnetic deflectors are made from a ferro-magnetic material, such as iron.
• the properties of the magnetic deflectors are selected such that the material, e.g. iron, is not saturated by the external magnetic field.
• the external magnetic field may be the earth magnetic field and or another external magnetic field, e.g. a magnetic field induced by a high-current cable.
• the properties of the magnetic deflectors are selected such that they do not saturate by magnetic fields that can be expected or defined by e.g. a standard or regulation.
• the two magnetic deflectors having the dimensions of 5 x 10 mm are made from iron and extend the length of the hydraulic cylinder.
• the length of a magnetic deflector is preferably longer than the magnetic detector, but may also be shorter depending on e.g. the material properties and/or the positioning of the magnetic deflector.
• the magnetic deflectors are fastened to the outside of the hydraulic cylinder in a symmetric way, as is shown in fig. 3b.
• the magnetic detector arrangement comprises three magnetic deflectors 7 positioned parallel to the magnetic sensor and symmetric to the symmetry axis 11 running through the sensor element 2 and the magnet 4.
• the three magnetic deflectors are fastened to the outside of the hydraulic cylinder in a symmetric way, with one deflector opposing the sensor and the other two positioned with an offset of 120 degrees around the cylinder, as is shown in fig. 4b.
• the magnetic deflectors do not need to be fixed to the hydraulic cylinder. As is shown in fig. 5, they may also be positioned around the cylinder in space, somewhat distance from the outside surface of the cylinder. This positioning may be advantageous in some installations, e.g. when the cylinder itself needs to be changed or maintained.
• Figs. 6 and 7 show embodiments with a tube-like magnetic deflector that will not disturb the magnetic sensor.
• the magnetic deflector is a tube with a cut-out extending the length of the magnetic deflector. The cut-out is in the order of 90 degrees and preferably in the range between 60 and 180 degrees.
• the magnetic deflector is a tube with a diameter that is large enough to enclose the complete cylinder with the magnetic detector arrangement. The distance between the tube and the sensor is chosen so that the tube does not disturb the sensor.
• magnétique deflectors prevent the piston rod from being magnetised by the external magnetic field. Since the magnetic deflectors direct the external magnetic field parallel to the sensor, the magnetic field will also be parallel to the piston rod. Since the piston rod does not move perpendicular to a magnetic field, the magnetisation of the piston rod will be greatly reduced.
• the magnetic element 4 comprises two permanent magnets .
• a schematic magnetic detector comprising two permanent magnets is shown in fig. 8.
• the magnets have approximately the same magnetic properties .
• the magnets are equally polarised and positioned next to each other in a symmetrical way with their symmetry axes parallel and with the polarisation in the same direction.
• the distance between the magnets is small compared with the size of the magnets .
• the distance between the magnets is selected so that the magnetic field is as wide as possible with an equal density. This is possible due to the fact that the magnetic field from the magnets will deform symmetrically in respect to a plane in between the magnets when positioned close to each other. By doing this, a well-defined magnetic field is obtained.
• This embodiment allows for an improved sensitivity of the magnetic detector arrangement.
• the optimal distance between the magnets depends on various magnetic properties of the magnets .
• the optimal distance is small or equal compared to the thickness of the magnets.
• the optimal distance for two ceramic type magnets with the size 12*6 mm and 4 mm thick can be between 0.9 mm to 4 mm when the two planes with the size 12*6 mm are side by side.
• the easiest way to obtain the optimal distance is by empirical measurements .
• the optimal distance between the magnets depends on various magnetic properties of the magnets.
• the optimal distance is small compared to the magnets .
• the optimal distance for two ceramic type magnets with the size 12*6*4 mm can be approximately 0.9 mm.
• the easiest way to obtain the optimal distance is by empirical measurements .
• the invention is not to be regarded as being limited to the embodiments described above, a number of additional variants and modifications being possible within the scope of the subsequent patent claims .
• the magnetic arrangement can, for example, also be used for other types of detectors or switches. 1 : Magnetic detector arrangement

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Condensed Matter Physics & Semiconductors (AREA)
• Engineering & Computer Science (AREA)
• Fluid Mechanics (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Actuator (AREA)
• Measuring Magnetic Variables (AREA)
• Measurement Of Length, Angles, Or The Like Using Electric Or Magnetic Means (AREA)

Priority Applications (1)

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Publications (1)

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Family Applications (1)

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Cited By (3)

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Citations (6)

Family Cites Families (1)

• 2005
  • 2005-12-02 SE SE0502659A patent/SE530319C2/sv unknown
• 2006
  • 2006-11-24 WO PCT/SE2006/001334 patent/WO2007064271A1/en active Application Filing
  • 2006-11-24 EP EP06824473A patent/EP1969318A4/de not_active Withdrawn

Patent Citations (6)

Non-Patent Citations (3)

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