EP1653089A1 - Device for determining the position of a moving piston rod with respect to a cylinder - Google Patents

Device for determining the position of a moving piston rod with respect to a cylinder Download PDF

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Publication number
EP1653089A1
EP1653089A1 EP05109726A EP05109726A EP1653089A1 EP 1653089 A1 EP1653089 A1 EP 1653089A1 EP 05109726 A EP05109726 A EP 05109726A EP 05109726 A EP05109726 A EP 05109726A EP 1653089 A1 EP1653089 A1 EP 1653089A1
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EP
European Patent Office
Prior art keywords
piston rod
region
hardened
metallic
sensor
Prior art date
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.)
Granted
Application number
EP05109726A
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German (de)
French (fr)
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EP1653089B1 (en
Inventor
Gopal S Revankar
Keith W Gray
Dale H Killen
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Deere and Co
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Deere and Co
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Priority to US10/974,330 priority Critical patent/US7116097B2/en
Application filed by Deere and Co filed Critical Deere and Co
Publication of EP1653089A1 publication Critical patent/EP1653089A1/en
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    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15BSYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B15/00Fluid-actuated devices for displacing a member from one position to another; Gearing associated therewith
    • F15B15/20Other details, e.g. assembly with regulating devices
    • F15B15/28Means for indicating the position, e.g. end of stroke
    • F15B15/2815Position sensing, i.e. means for continuous measurement of position, e.g. LVDT
    • F15B15/2869Position sensing, i.e. means for continuous measurement of position, e.g. LVDT using electromagnetic radiation, e.g. radar or microwaves
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15BSYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B15/00Fluid-actuated devices for displacing a member from one position to another; Gearing associated therewith
    • F15B15/20Other details, e.g. assembly with regulating devices
    • F15B15/28Means for indicating the position, e.g. end of stroke
    • F15B15/2815Position sensing, i.e. means for continuous measurement of position, e.g. LVDT
    • F15B15/2846Position sensing, i.e. means for continuous measurement of position, e.g. LVDT using detection of markings, e.g. markings on the piston rod
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15BSYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B15/00Fluid-actuated devices for displacing a member from one position to another; Gearing associated therewith
    • F15B15/20Other details, e.g. assembly with regulating devices
    • F15B15/28Means for indicating the position, e.g. end of stroke
    • F15B15/2815Position sensing, i.e. means for continuous measurement of position, e.g. LVDT
    • F15B15/2861Position sensing, i.e. means for continuous measurement of position, e.g. LVDT using magnetic means

Abstract

The invention relates to a device for detecting the position of a movable piston rod (28, 128, 228) relative to a cylinder (12).
It is proposed that the piston rod (28, 128, 228) has a first hardened metallic region (36, 136, 236), and a second hardened metallic region (34, 134, 234), the depths of which differ from one to the other Detecting an eddy current or induced electromagnetic field sensor (22) is provided, which detects when at least one of the hardened metallic regions (34, 36, 134, 136, 234, 236) in the detection range of the sensor (22) is located, and that Data processor (52) operable to determine the longitudinal position of the piston rod (28, 128, 228) relative to the cylinder (12) based on the signal of the sensor (22).

Description

  • The invention relates to a device for detecting the position of a movable piston rod relative to a cylinder.
  • State of the art
  • Prior art devices for measuring the position of a piston within a cylinder use a magnet embedded in the piston and one or more Hall effect sensors that sense the magnetic field. In practice, such devices are limited to cylinders with a limited path and may require expensive magnets with strong magnetic fields. Other known devices for measuring the position of a piston within a cylinder use magnetostrictive sensors, which require the installation of multiple magnets in the cylinder. Since some effort is required to process the magnet pick-up and other work, the provision of known means for measuring the position of the piston may prove too costly and inconvenient for certain piston rods.
  • Object of the invention
  • The object underlying the invention is to provide an improved, reliable and economical technique for determining the position of a piston or other element.
  • This object is achieved by the teaching of claim 1, wherein in the other claims features are listed, which further develop the solution in an advantageous manner.
  • It is proposed to define a piston rod with to provide hardened metallic regions. The piston rod has a first hardened metallic region extending between the surface of the piston rod to a first radial depth below the surface of the piston rod and located at a first radial position. The piston rod further has a second hardened metallic region extending between the surface of the piston rod to a second radial depth below the surface of the piston rod and located at a second radial position. The second radial depth differs from the first radial depth. A sensor detects an eddy current and / or an electromagnetic field whose properties depend on the depths of hardening to detect when one of the mentioned regions is within the detection range of the fixed sensor. A data processor determines the longitudinal position of the piston rod relative to the cylinder based on the signal from the sensor.
  • embodiments
  • In the drawings, five embodiments of the invention described in more detail below are shown. It shows:
  • Fig. 1
    a perspective view of a device according to the invention for detecting the axial position of a piston rod (or an attached element),
    Fig. 2
    a cross-sectional view of the device of Figure 1,
    Fig. 3
    a cross-sectional view of the piston rod along the reference lines 3-3 of Figure 2,
    Fig. 4
    a cross-sectional view of the piston rod along the reference lines 4-4 of Figure 2,
    Fig. 5
    a cross-sectional view of the piston rod along the reference lines 5-5 of Figure 2,
    Fig. 6
    a cross-sectional view of the piston rod in a position of minimal axial displacement,
    Fig. 7
    a cross-sectional view of the piston rod in a position of maximum axial displacement,
    Fig. 8
    FIG. 3 is a cross-sectional view of a portion of the piston rod of FIGS. 1 and 2;
    Fig. 9
    a flow chart of a method according to the invention for detecting the axial position of a piston rod (or an attached element),
    Fig. 10
    a graph of the hardening depth versus the relative longitudinal displacement according to a second embodiment of the invention,
    Fig. 11
    a graph of the hardening depth versus the relative longitudinal displacement according to a third embodiment of the invention,
    Fig. 12
    a cross-section through a second embodiment of a device according to the invention for detecting the axial position of a piston rod (or an attached element), and
    Fig. 13
    a cross section through a third embodiment of a device according to the invention for detecting the axial position of a piston rod (or an attached element).
  • In the figures, the same reference numerals designate the same elements.
  • FIG. 1 shows a perspective view of an embodiment of a device according to the invention Detecting the axial position of a piston rod 28 (or an attached member 10) against a cylinder 12 (eg, a hydraulic cylinder). The cylinder 12 is cut open to better show the components of FIG. An element 10, such as a piston, may be coupled to one end of the piston rod 28. The element 10 is displaceable in an axial direction within the cylinder 12. The limited by the element 10 and the interior of the cylinder 12 volume is referred to as chamber 24. For example, if the element 10 and the piston rod 28 are parts of a hydraulic cylinder or assembly, the chamber would contain hydraulic fluid or oil.
  • A bearing 18 is connected to the cylinder 12. For example, it is secured between the cylinder 12 and the piston rod 28 (eg, pressed or screwed into the interior of the cylinder 12). The bearing 18 houses one or more seals (eg, an inner seal 14 and an outer seal 16) and a sensor 22. The bearing 18 and the cylinder 12 allow the attachment of an inner seal 14 and an outer seal 16. In a Embodiment, the seals 14, 16 are lubricated to reduce the friction at the interface between the bearing 18 and the piston rod 28. The bearing 18 can also serve as a guide for the piston rod 28. The bearing 18 allows movement of the piston rod 28 in its longitudinal direction relative to the cylinder 12th
  • Although a sensor 22 may be received in the bearing 18 as shown in FIG. 1, in other embodiments, the sensor 22 may be secured to a different location of the cylinder 12. For example, in another embodiment, the sensor 22 could include a ring having a central opening disposed about the piston rod 28. In yet another embodiment, the sensor 22 is integrated with the inner seal 14 or the outer seal 16.
  • The sensor 22 allows detection of the axial position of the piston rod 28 relative to the cylinder 12. The sensor 22 may comprise a coil, an inductive probe or the like, which is acted upon by an oscillator 53 of the analyzer 55 with an AC or radio frequency signal.
  • The analyzer 55 is electrically or electromagnetically coupled to the sensor 22 and includes the oscillator 53 for generating an AC signal (eg, radio frequency signal), an electrical energy detector 50 for detecting changes in the electromagnetic field or eddy current field caused by the generated signal around the sensor 22, and a data processor 52 for correlating the changes in the eddy current field with a change in the axial position of the piston rod 28. The oscillator 53 may receive one or more signals within a frequency range (eg 10 Hz to 10 kHz). generate to bias the sensor 22 and to cause the radiation of an eddy current field or electromagnetic radiation.
  • In one embodiment, the electrical energy detector 50 includes a voltmeter connected in parallel with an inductor or coil of the sensor 22. In another embodiment, the electrical energy detector 50 includes an ammeter connected in series with the sensor 22. The electrical energy detector 50 may be connected to an analog-to-digital converter or the sensor 22 provides an analog output signal to the data processor 52.
  • The data processor 52 determines the axial or longitudinal position of the piston rod 28 relative to the cylinder 12 at each time based on the detected eddy current or the detected electromagnetic field detected by the electrical energy detector 50. Advantageously, the sensor 22 is not within the pressurized state Chamber 24 of the cylinder 12 is arranged and therefore need not withstand any thermal stress or existing in the chamber 24 pressure.
  • The thickness and shape of the defined hardened region of the piston rod 28 may vary along the length of the piston rod 28 according to different embodiments. For example, an induction hardening process or case hardening process may be used to vary the depth of the defined, hardened region of the piston rod. Curing is any process that increases the hardness of a metal or alloy. For example, a metal or alloy may be heated to a target temperature or temperature range and cooled at a certain rate or for a given cooling time. Case hardening refers to the addition of carbon to a surface region of an iron alloy to produce a carbon-enriched iron alloy, and a heat treatment (eg, by induction heating) of the entire surface of the carbon-enriched iron alloy or a part thereof. The curing process can be used to alter the magnetic permeability of the metal or alloy or carbon-enriched iron alloy while leaving the electrical conductivity substantially unchanged.
  • Induction hardening can be used to define the defined hardened region by controlling a depth of cure by changing the induction current. For example, the induction frequency may be varied linearly as the induction coil moves axially along the length of the piston rod 28 to achieve a non-linear depth of case hardening along the length of the piston rod 28. In another example, the induction frequency may be varied to achieve a linear variation of the hardened depth of use along the piston rod 28. The following variables can be used Induction hardening of the piston rod 28 influences: (1) the power density induced in a surface layer of the piston rod 28, (2) the distance between the induction coil and the piston rod 28, (3) concentricity or coaxial alignment between the induction coil and the piston rod 28, (4) Coil voltage, (5) coil design, (6) speed of movement of the coil with respect to the surface of the piston rod 28, and (7) environmental conditions including room temperature, humidity and air turbulence.
  • The thickness (ie depth) and shape of the defined hardened region may cause variations in permeability (from a surface to a radial depth spaced therefrom) or other variations in material that affect the propagation of eddy currents along the length of the piston rod which may be caused by the analyzer 55 can be detected. In one embodiment of the invention, as illustrated in Figure 1 in conjunction with Figures 2 and 8, the piston rod 28 at a first position 40 in the longitudinal direction, a first, hardened metallic region 36 extending from a surface of the piston rod 28th extends to a first radial depth 80 below the surface. The piston rod 28 has at a second position 39 in the longitudinal direction and a third position 38, a second, hardened metallic region 34 which extends from a surface of the piston rod 28 to a second radial depth 80 below the surface. The second radial depth 82 differs from the first radial depth 80. The depth of an intermediate metal region 51 between the first hardened metallic region 36 and the second hardened metallic region 34 varies in a substantially linear manner, as illustrated, for example, in the cross section of FIG , Although the metallic intermediate region 51 becomes increasingly thick towards the outside from a longitudinal position 40 of the piston rod 28, in other embodiments it could become thicker internally.
  • The sensor 22 detects an eddy current or a electromagnetic field to detect alignment of a portion of the defined metallic region with a fixed detection region at the respective time. For example, the sensor 22 detects a first eddy current or a first electromagnetic field when the piston rod 28 has a first longitudinal position 40 in which the sensor 22 is aligned with the first hardened metallic region 36. The sensor 22 detects a second eddy current or a second electromagnetic field when the piston rod 28 has a first longitudinal position 39 in which the sensor 22 is aligned with the second hardened metallic region 34. The change in the eddy current or electromagnetic field between the first eddy current and the second eddy current indicates the movement or positional change of the piston rod 28. The electrical energy detector 50 measures the change in eddy current or electromagnetic field associated with the axial displacement of the piston rod 28 by monitoring the current or voltage induced in the sensor 22. The data processor 52 may store a reference table or database in which axial positions of the piston rod 28 are stored relative to measured current values. The measured current value is compared with the reference current value to determine the axial position of the piston rod 28.
  • If the depth of the defined, hardened regions varies symmetrically about a central region 40 of the piston rod 28, as shown in Figure 1, there is potential ambiguity for each equal thickness of the hardened region along the piston rod 28. To distinguish the equivalent regions alternatively or cumulatively different techniques are used. According to a first technique, a first slope of a defined hardened region between a central region (eg, the first longitudinal position 40) of the piston rod 28 and an end (eg, the second longitudinal position 39) may be hardened by a second slope of the defined one Region between the middle region of the piston rod 28 and the opposite lying end (eg, the third longitudinal position 38), z. B. be steeper. According to a second technique, an additional sensor may sense the direction of axial movement of the piston rod 28 to resolve the ambiguity between the two equivalent thicknesses of the hardened region along the piston rod 28. According to a third technique, an additional sensor may be used when the piston rod 28 reaches the limit of the range of movement in an axial direction or in the opposite direction. For example, a contact sensor may be connected to the end of the bearing 18 so that it is contacted at the end of its range of motion by the element 10 (piston) and provides an electrical signal indicative of such contact. According to a fourth technique, only half the axial displacement between the first longitudinal position 40 and the second longitudinal position 39 or between the first longitudinal position 40 and the third longitudinal position 38 is detected.
  • The profile or cross section of the defined hardened region or intermediate metal region 51 between the first hardened metallic region 36 and the second hardened metallic region 34 may vary in different embodiments of the piston rod 28. In a first embodiment of the piston rod 28, the intermediate region 51 between the first hardened metallic region 36 and the second hardened metallic region 34 is linearly inclined in accordance with FIGS. 1, 2 and 8. In a second embodiment, a metallic intermediate region 51 of the piston rod 28 varies between the first hardened metallic region 36 and the second metallic region 34 corresponding to 1 / x 2 , where x is a longitudinal distance along the piston rod 28. The second embodiment corresponds to the cure depth profile of FIG. 10. In a third embodiment of the piston rod, an intermediate metal region 51 of the piston rod 28 varies between the first hardened metallic region 36 and the second hardened metallic region 34 corresponding to 1 / √f, where f is the frequency of the induction current used to harden the intermediate metal region 51. The third embodiment corresponds to the cure profile of FIG. 11. In a fourth embodiment, the piston rod 28 may be mechanically prevented from rotating to inhibit rotation relative to the cylinder 12 if the defined hardened region is not substantially within a cross-section through the piston rod 28 is symmetrical. In a fifth embodiment of a piston rod 28, the first hardened metallic region 36 and the second hardened metallic region 34 are formed according to the following equation: y = ρ / π μ 0 μ f .
    Figure imgb0001

    where p is the resistivity of the piston rod 28, μ o is the magnetic permeability of the vacuum, μ is the relative permeability of the piston rod 28, and f is the frequency of the induction current. In a sixth embodiment of the piston rod 28, the first hardened metallic region 36 and the second hardened metallic region 34 are formed according to the following equation: y = k f .
    Figure imgb0002

    where k is a constant based on a metallic material at a given temperature range and f is the frequency of the induction current. Any of the previously described alternative embodiments of the piston rod 28 may be used, for example, in conjunction with the configuration of FIGS. 1 and 2. In addition, some of the aforementioned alternative embodiments will be described in more detail with reference to FIGS. 10 and 11.
  • Although the piston rod 28 may be constructed of different metals or alloys that fall within the scope of the invention, the piston rod 28 is in one An embodiment of steel or an iron-based alloy that may be clad with a protective metallic plating material (eg, nickel and chromium). The metallic plating material is not shown in FIGS. 1 and 2. When the metallic plating material is attached to an outer surface of the piston rod 28, the thickness of the plating should be substantially uniform so as to avoid disturbances in the eddy currents or the electromagnetic field induced in the sensor 22.
  • FIG. 2 shows a middle axial position 32 or displacement of the piston rod 28 between two opposite movement limits. In FIG. 2, the first hardened metallic region 36 is arranged in the detection region of the sensor 22. The first hardened metallic region 36 is associated with a first longitudinal position 40 of the piston rod 28. The second hardened metallic regions 34 are on both sides of the first hardened metallic region 36.
  • 3 shows a cross section of the piston rod 28 along the line 3-3 at the second longitudinal position 39 of the piston rod 28. The second longitudinal position 39 is within the second hardened region 34 of the piston rod 28. The second hardened metallic region 34 covers the piston rod core 30th
  • 4 shows a cross-section of the piston rod 28 along the line 4-4 at the first longitudinal position 40 of the piston rod 28. The first longitudinal position 40 lies within the first hardened region 36 of the piston rod 28. The first hardened metallic region 36 covers the piston rod core 30.
  • Figure 5 shows a cross-section of the piston rod 28 along the line 5-5 at the third longitudinal position 38 of the piston rod 28. The third longitudinal position 38 lies within the second hardened region 34 of the piston rod 28. The third hardened metallic region 34 covers the piston rod core 30 and is located at the opposite end of the piston rod 28 with respect to the second longitudinal position 39.
  • Figure 6 shows the piston rod 28 in a minimum axial position 62 or dislocation at a corresponding limit of the range of motion. In FIG. 6, the third longitudinal position 38 of the piston rod, which lies within the second hardened metallic region 34, is arranged in the detection region of the sensor 22.
  • Figure 7 shows the piston rod 28 in a maximum axial position 64 or dislocation at a corresponding limit of the range of motion. In FIG. 7, the second longitudinal position 39 of the piston rod 28, which lies within the second hardened metallic region 34, is arranged in the detection region of the sensor 22.
  • FIG. 8 shows a first radial depth 80 that differs from a second radial depth 82. The first radial depth 80 is associated with the first hardened metallic region 36. The second radial depth 82 is associated with the second hardened metallic region 34. Although an intermediate region 51 between the first hardened metallic region 36 and the second hardened metallic region 34 varies in a substantially linear manner, as shown in Figure 8, it could also vary according to other profiles (e.g., due to the induction frequency of the Induction hardening), some of which have been discussed in connection with FIG. In practice, the actual depth of use or the defined hardened metallic region may differ somewhat from a theoretical, linear variation over the length of the piston rod 28.
  • FIG. 9 shows a method for detecting the position of the element 10 beginning in step S100, in which a piston rod 28 having a first hardened metallic region 36 between the surface of the piston rod 28 to a first radial depth 80 below the surface at a first longitudinal position 40 and with a second hardened metallic region 34 between the surface of the piston rod 28 to in a second radial depth 82 is provided below the surface at a second longitudinal position 39. The second radial depth 82 differs from the first radial depth 80. The first radial depth 80 in this example, as shown in FIG. 8, is considerably larger than the second radial depth 82, resulting in a significant variation in FIG Permeability between the first radial depth 80 and the second radial depth 82, which is detectable by the sensor 22.
  • In step 102, a sensor 22 detects an eddy current to detect alignment of a defined, hardened metallic region 26 with a solid detection region at a particular time. For example, the sensor 22 detects an eddy current or an electromagnetic field, which indicates alignment of at least the first hardened metal region 36, the second hardened metal region 34, and the metallic intermediate region 51 with the solid detection region at each time point.
  • In step 104, the data processor 52 determines an axial position or longitudinal position of the piston rod 28 relative to the cylinder 12 at each time based on the detected eddy current or electromagnetic field. For example, the data processor 52 detects the sensed eddy current, converts the sensed eddy current into a digital signal or digital value, and compares the digital signal with reference current values in a table or database. The corresponding axial position of the piston rod 28 corresponds to the determined reference current value that comes closest to the detected current value.
  • FIG. 10 illustrates a possible depth profile of the defined hardened metallic region 26 along the piston rod 28. Relative longitudinal or axial displacement along the piston rod 28 is shown on the x-axis. The hardened depth is shown on the y-axis. A middle region of the piston rod 28 has a maximum Hardening depth, which is shown as y m . The depth profile of FIG. 10 is referred to as a 1 / x 2 profile and is formed by the attachment of a metallic intermediate region 51 between the first hardened metallic region 36 and the second hardened metallic region 36, which varies according to 1 / √f, where f is the Frequency of the induction current, which is used to harden the intermediate metal region 51. The defined hardened metallic region of FIG. 10 (eg, first hardened metallic region 36, intermediate metal region 51, and second hardened metallic region 34) are formed according to the following equation: y = ρ / π μ 0 μ f .
    Figure imgb0003

    where p is the resistivity of the piston rod 28, μ o is the magnetic permeability of the vacuum, μ is the relative permeability of the piston rod 28, and f is the frequency of the induction current.
  • Figure 11 illustrates a possible depth profile of the defined hardened metallic region 26 along the piston rod 28. The longitudinal or axial relative displacement along the piston rod 28 is shown on the x-axis. The hardened depth is shown on the y-axis. One end of the piston rod 28 has a maximum depth of cure, shown as y m . The depth profile of Figure 11 is referred to as a 1 / √x profile. In FIG. 11, an intermediate metal region 51 varies corresponding to 1 / √f, where f is the frequency of the induction current used to harden the intermediate metal region 51. The defined hardened metallic region of Figure 11 (eg, first hardened metallic region 36, intermediate metal region 51, and second hardened metallic region 34) are formed according to the following equation: y = ρ / π μ 0 μ f .
    Figure imgb0004

    where p is the resistivity of the piston rod 28, μ o is the magnetic permeability of the vacuum, μ is the relative permeability of the piston rod 28, and f is the frequency of the induction current.
  • The piston rod 128 of FIG. 12 is similar to the piston rod 28 of FIG. 2, except that the defined hardened metallic region of FIG. 12 includes a first hardened metallic region 134, a second hardened metallic region 136, and a hardened metallic intermediate region 135.
  • Figure 12 allows two alternative embodiments. In a first embodiment, the first hardened metallic region 134 includes a substantially rectangular strip having a first radial depth, while the second hardened metallic region 136 is spaced from the first hardened metallic region 134 and has a second radial depth that is different from the first radial depth is different. The second radial depth may be greater or less than the first radial depth. Regardless of the radial depths of the rectangular strips, each rectangular strip on the piston rod 128 may be axially longer or shorter than the other rectangular strip. The hardened metallic intermediate region 135 is interposed between the first hardened metallic region 134 and the second hardened metallic region 136. The hardened metallic intermediate region 135 is thinner than the first hardened metallic region 134 and thinner than the second metallic region 136.
  • In a second embodiment of a piston rod 128 of FIG. 12, the first hardened metallic region 134 is substantially annular with a first radial depth and the second hardened metallic region 136 is also annular and spaced from the first metallic region 134. The hardened metallic intermediate region 135 lies between the first hardened metallic region 134 and the second hardened metallic region 136. The second radial depth differs from the first radial depth. Regardless of the radial depths of the annular regions, each annular region on the piston rod 128 may be axially longer or shorter than the other annular region.
  • When the first hardened metallic region 134 is aligned with the sensor 22 at a first longitudinal position 138, the piston rod 128 has a known axial displacement relative to the cylinder. When the intermediate metal hardened region 135 is aligned with the sensor 22, the piston rod 128 has a second known axial displacement (eg, an axial displacement region) relative to the cylinder 12. When the second hardened metallic region 136 engages at a second longitudinal position 139 the sensor 22, the piston rod 128 has a third known axial displacement relative to the cylinder 12. The configuration of FIG. 12 is useful, for example, for providing electronic stops for the element 10 moving in the cylinder 12.
  • The piston rod 228 of FIG. 13 is similar to the piston rod 28 of FIG. 2, except that the defined hardened metallic region of FIG. 13 has a first hardened metallic region 234, a second hardened metallic region 236, and a hardened metallic intermediate region 235.
  • FIG. 13 enables two alternative embodiments. In a first embodiment, the first hardened metallic region 234 includes a substantially rectangular strip having a first radial depth, while the second hardened metallic region 236 is spaced from the first hardened metallic region 234 and has a second radial depth that is different from the first radial depth is different. The second radial depth may be greater or less than the first radial depth. Regardless of the radial depths of the rectangular strips, each rectangular strip on the piston rod 228 may be axially longer or shorter than the other rectangular strip. The hardened metallic intermediate region 235 lies between the first hardened metallic region 234 and second hardened metallic region 236. The hardened metallic intermediate region 235 is thicker than the first hardened metallic region 134 and thicker than the second metallic region 136.
  • In a second embodiment of a piston rod 228 of FIG. 13, the first hardened metallic region 234 is substantially annular with a first radial depth and the second hardened metallic region 236 is substantially annular and spaced from the first metallic region 234. The hardened intermediate metal region 235 lies between the first hardened metallic region 234 and the second hardened metallic region 236. The second radial depth is different from the first radial depth. Regardless of the radial depths of the annular regions, each annular region on the piston rod 228 may be axially longer or shorter than the other annular region.
  • When the first hardened metallic region 234 is aligned with the sensor 22 at a first longitudinal position 238, the piston rod 228 has a known axial displacement relative to the cylinder. When the intermediate metal hardened region 235 is aligned with the sensor 22, the piston rod 228 has a second known axial displacement (eg, an axial displacement region) relative to the cylinder 12. When the second hardened metallic region 236 engages at a second longitudinal position 239 aligned with the sensor 22, the piston rod 228 has a third known axial displacement relative to the cylinder 12. The configuration of Figure 13 is useful, for example, to provide electronic stops for the element 10 moving in the cylinder 12.
  • All of the foregoing embodiments of the means and method for detecting the position of a piston rod 28, 128, 228 (or member 10 attached thereto) utilize sensors mounted outside of the cylinder chamber 24. There is therefore no special sealing of the cylinder chamber 24 is required. It detects electromagnetic fields that be induced on the surface of the piston rod 28, 128, 228 within a penetration depth, so that no contact with the piston rod is needed and no moving parts would be required, which adversely affect the reliability. The device can also be retrofitted to existing cylinders.

Claims (8)

  1. Device for detecting the position of a movable piston rod (28, 128, 228) relative to a cylinder (12), characterized in that the piston rod (28, 128, 228) has a first hardened metallic region (36, 136, 236) extending extending from the surface of the piston rod (28, 128, 228) to a first radial depth (80) below the surface of the piston rod (28, 128, 228) and having a second hardened metallic region (34, 134, 234), extending from the surface of the piston rod (28, 128, 228) to a second radial depth (82) below the surface of the piston rod (28, 128, 228), the first depth (80) extending from the second depth (80). 82), there is provided a sensor (22) arranged to detect an eddy current or induced electromagnetic field, which detects when at least one of the hardened metallic regions (34, 36, 134, 136, 234, 236) in the detection area of the sensor ( 22), and that one Data processor (52) operable to determine the longitudinal position of the piston rod (28, 128, 228) relative to the cylinder (12) based on the signal of the sensor (22).
  2. Device according to claim 1, characterized in that a hardened metallic intermediate region (51) is present between the first region (36) and the second region (34) whose hardening depth varies in a substantially linear manner.
  3. Device according to claim 1, characterized in that a hardened metallic intermediate region (51) is present between the first region (36) and the second region (34) whose hardening depth varies substantially to 1 / x 2 or 1 / √x, x a longitudinal direction of the Piston rod (28) is measured distance.
  4. Device according to claim 1, characterized in that the first and second metallic hardened regions (134, 136) are rectangular.
  5. The device of claim 4, characterized in that the first metallic hardened region (136) has a first axial length that is different from the second axial length of the second metallic hardened region (134).
  6. Device according to claim 1, characterized in that the first and second metallic hardened regions (234, 236) are annular.
  7. The device of claim 6, characterized in that the first metallic hardened region (236) has a first axial length that is different from the second axial length of the second metallic hardened region (234).
  8. Device according to one of the preceding claims, characterized in that the metallic, hardened regions (34, 36, 134, 136, 234, 236) are produced by induction hardening.
EP20050109726 2004-10-27 2005-10-19 Device for determining the position of a moving piston rod with respect to a cylinder Expired - Fee Related EP1653089B1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
US10/974,330 US7116097B2 (en) 2004-10-27 2004-10-27 System and method for detecting the axial position of a shaft or a member attached thereto

Publications (2)

Publication Number Publication Date
EP1653089A1 true EP1653089A1 (en) 2006-05-03
EP1653089B1 EP1653089B1 (en) 2008-12-31

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CN106482627A (en) * 2016-09-22 2017-03-08 大连理工大学 A kind of testing stand for measuring bearing Radial windage and method

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DE502005006367D1 (en) 2009-02-12
US7116097B2 (en) 2006-10-03
US20060087313A1 (en) 2006-04-27

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