EP0306507B1 - A hydraulic cylinder with a built-in electric piston position indicator - Google Patents

A hydraulic cylinder with a built-in electric piston position indicator Download PDF

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Publication number
EP0306507B1
EP0306507B1 EP19880902110 EP88902110A EP0306507B1 EP 0306507 B1 EP0306507 B1 EP 0306507B1 EP 19880902110 EP19880902110 EP 19880902110 EP 88902110 A EP88902110 A EP 88902110A EP 0306507 B1 EP0306507 B1 EP 0306507B1
Authority
EP
European Patent Office
Prior art keywords
piston
hydraulic cylinder
position indicator
cylinder
housing
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.)
Expired
Application number
EP19880902110
Other languages
German (de)
English (en)
French (fr)
Other versions
EP0306507A1 (en
Inventor
Niels Hvilsted
Kaj Pedersen
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Individual
Original Assignee
Individual
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 Individual filed Critical Individual
Priority to AT88902110T priority Critical patent/ATE65302T1/de
Publication of EP0306507A1 publication Critical patent/EP0306507A1/en
Application granted granted Critical
Publication of EP0306507B1 publication Critical patent/EP0306507B1/en
Expired legal-status Critical Current

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Classifications

    • 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
    • F15B15/2892—Means for indicating the position, e.g. end of stroke characterised by the attachment 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

Definitions

  • the invention relates to a hydraulic cylinder with a built-in inductive piston position indicator transmitting an electric signal corresponding to the actual piston position, said piston position indicator being received in a longitudinal opening extending in the piston and piston rod of the hydraulic cylinder and comprising a core made of an electrically conductive material and an induction coil, in which the core is allowed to reciprocate freely, said core is connected to the piston rod of the hydraulic cylinder, and said induction coil is connected to the housing of the hydraulic cylinder or vice versa.
  • the metal particles will be able to become fixed on the induction coil itself or between this and the opening in the piston rod and thereby being able to short-circuit the induction coil with the consequense of a breakdown of the inductive piston position indicator.
  • the enclosed amount of the hydraulic oil which is always present in the tube of the piston position indicator in front of the steel rod, cannot quickly enough flow out and in between the inside of the tube and the cylinder room outside the tube.
  • this inductive piston position indication is to work under the high working pressures of 2-300 bar usually applying to hydraulic cylinders and especially pressure peaks of up to 6-800 bar and piston speeds of up to 15 m per second there is consequently every probability that it quickly breaks down.
  • the by the piston movement of the piston rod in the cylinder uncovered piece of the induction coil in the cylinder is also very much exposed to outside coming noise signals which may cause incorrect feedbacks from the piston position indicator.
  • This hydraulic cylinder with built-in inductive piston position indicator is for that reason only suited to work with especially pure hydraulic oil and under conditions with very low working pressures for the hydraulic oil and very low piston speeds.
  • the object of the invention is to provide a hydraulic cylinder with built-in inductive piston position indicator of the type mentioned in the introduction which can stand up to the high working pressures usually applying to hydraulic cylinders without involving larger outer dimensions than corresponding cylinders not including built-in position indicators, and which cylinder is furthermore reliable in use and inexpensive to manufacture.
  • the hydraulic cylinder according to the invention is characterised in that the induction coil is secured inside and extends over the entire length of a tubular housing which liquid tightly surrounds the core.
  • a hydraulic cylinder with a built-in inductive piston position indicator is provided, which is working most reliable under all conditions and especially under the high working pressures from the hydraulic oil usually applying to hydraulic cylinders.
  • This is especially due to the fact that the mutual movement between the core and the induction coil of the piston position indicator is neither affected by the hydraulic oil itself nor by the impurities present impurities, e.g. the always present torn off metal particles, as the core and the induction coil of the piston postion indicator are protected against coming into contact with the hydraulic oil by means of the tubular housing of the position indicator.
  • the by the piston position indicator transmitted signal will not be affected by outside coming electric noise signals either, as the by the movement of the piston in the cylinder uncovered and no longer by the piston rod protected piece of the induction coil will always be encapsulated in the tubular housing of the piston position indicator.
  • the housing of the position indicator may be connected to the housing of the hydraulic cylinder, preferably by way of a pressure and liquitight connection in the end cover of the hydraulic cylinder, and the core of the position indicator may be connected to the piston rod of the hydraulic cylinder, preferably by means of a rod screwed into outer securing means fixed on the end of the piston rod of the hydraulic cylinder.
  • a particularly simple securing of the position indicator is obtained as it is particularly easy and quick to replace said indicator, e.g. at service check.
  • the conduits always extending out of one end of the housing of the position indicator can in a simple manner extend outwards directly through the end cover of the cylinder, said housing of the position indicator being secured in the end cover of the hydraulic cylinder.
  • the housing of the position indicator may extend into the end covers of the hydraulic cylinder, whereby the movement of the core is limited to an area in the housing of the position indicator spaced from the ends of said position indicator.
  • the core can only move inside the most exact measuring area of the position indicator, said core never moving in the measuring areas at the ends of the position indicator, which as far as inductive position indicators are concerned are the most inaccurate or "unlinear" areas.
  • the opening in the piston of the hydraulic cylinder may be pressure and liquid-tightly closed towards the interior of the cylinder, preferably by means of gaskets between the piston and the housing of the position indicator. In this manner the area of the position indicator ⁇ in which the piston rod thereof extends through the housing thereof ⁇ is not affected by the pressure and the oil of the hydraulic cylinder.
  • the cylinder may be provided with one or more electric position indicators, whereby each indicator indicates a predetermined position of the piston, and the electric signal transmitted by these position indicators may co-operate with the signal of the pistion position indicator in achieving a calibration or zeroing of the signal of the piston position indicator each time the piston of the hydraulic cylinder is in one of these predetermined pistion positions.
  • a particularly accurate measuring of the piston position is obtained as the signal of the piston position indicator is calibrated each time the piston of the hydraulic cylinder is at one of the predetermined piston positions.
  • the electric position indicators may be inductive sensors provided in through-openings in the end covers of the cylinder, said openings being pressure and liquid-tightly closed towards the interior of the cylinder.
  • the cylinder is particularly simple to manufacture, and the signals transmitted by the inductive sensors are particularly suited for co-operating with signals transmitted by other electric position indicators.
  • the hydraulic cylinder 1 of Fig. 1 comprises a cylinder housing 3, an end cover 4, 5 secured in each end of the cylinder housing 3 preferably by means of gluing or welding, and a piston 6 present in the cylinder housing 3 and mounted on a piston rod 7 extending through a through opening in one end cover 4.
  • the cylinder 1 has a stroke A and is illustrated with the piston in the bottom position.
  • the end cover 5 of the cylinder 1 and the end of the piston rod 7 opposite the piston are provided, preferably by way of welding, with outer securing means 8 and 9 for the outward securing of the cylinder housing 3 and the piston rod 7.
  • the hydraulic cylinder 1 is provided with in- and outlet gates 10, 11 for hydraulic oil, whereby the reciprocating movement of the piston 6 through the cylinder 1 can be controlled.
  • the piston 6 is furthermore provided with one or more circumferential recesses 12 receiving rings preferably of rubber for the sealing towards the inner surface of the cylinder housing 3.
  • the piston rod 7 extends through one 4 of the end covers of the cylinder 1, and said end cover 4 is also provided with one or more circumferential recesses 13 receiving the rubber ring, whereby the interior of the cylinder is pressure and liquid-tightly closed.
  • the piston rod 7 is preferably a steel pipe through which a piston position indicator 20 extends, cf. Figs. 1 and 2.
  • the piston position indicator of an advantageous embodiment according to the invention is an inductive position indicator 20 comprising an outer housing 21 in the form of a steel pipe.
  • the inductive position indicator comprises furthermore a rod 28 extending from one end of the housing 21.
  • the outer end of this rod 28 is provided with threads 29 and the inner end thereof is provided with a core 22 of an electrically conductive material.
  • An inductance coil 23 extends upwards along the inner surface of the housing and in the entire length of the housing 21.
  • Electric signals of volumes corresponding to the distance B or C of the core 22 from predetermined reference positions are transmitted by the position indicator 20 through conduits 27 in response to the position of the core 22 in said position indicator.
  • the inductive position indicator 20 is preferably of the type described in Danish Patent Application No. 335/85.
  • the housing of the piston position indicator 20 is secured by means of a Seeger ring 25 in the end cover 5 and is pressure and liquidtightly closed therein by means of a gasket 26.
  • the rod 28 of the position indicator 20 is screwed into the securing means 8 by means of the threaded connection 29, said securing means 8 being secured on the outer end of the piston rod 7.
  • inductive sensors 15 are provided in-through-openings 18 in the end covers 4, 5 of the cylinder 1.
  • the piston 6 of the cylinder 1 is furthermore made completely or partially of an electrically conductive material.
  • the openings 18 are pressure and liquid-tightly closed towards the interior of the cylinder 1 by means of preferably ceramic plates, e.g. as described in Danish printed accepted specification No. 150.225.
  • Fig. 3 shows how the ceramic plate 17 is situated in the end cover 5.
  • the inductive sensors 15 emit a magnetic field extending through the ceramic plates 17 and into the interior of the cylinder 1. The magnetic field is altered when the piston 6 enters therein and is situated immediately adjacent its extreme position at the end cover 4 or 5. The latter causes transmission of an altered electric signal from the sensor 15
  • the conduits 16 and 27 extend from the inductive sensors 15 and the piston position indicator 20, respectively, and out of the end covers 4 and 5 of the cylinder through the openings 18.
  • the conduits 16 and 27 are optionally connected through an interface or a signal amplifier to a signal processing or proces controlling equipment, e.g. a PLC control, IPC control, a PC or an industrial microcomputer.
  • a signal processing or proces controlling equipment e.g. a PLC control, IPC control, a PC or an industrial microcomputer.
  • the altered electric signal emitted by the inductive sensors 15 is used to cause a very accurate zeroing or calibration of the signal from the inductance piston position indicator 20. In this manner it is never necessary to measure directly on the cylinder in order to determine the exact position of the piston. It can also be considered an extra security that an unambigous signal independent of the piston position indicator is emitted each time the piston 6 is at one of its extreme positions.
  • Fig. 3 illustrates an embodiment substantially corresponding to the embodiment of Fig. 1, apart from the feature that circumferential recesses are shaped inside the piston rod 7 or the piston 6. Gaskets 14 are situated in these recesses and close pressure and liquid-tightly towards the interior of the cylinder 1. In this manner the area of the piston position indicator 20 ⁇ in which the rod 28 leaves the housing 21 ⁇ is not affected by the pressure nor the oil present in the cylinder 1. In Fig. 3 the housing 21 of the piston position indicator 20 is furthermore shown in a position where it is secured in the end cover 5 by means of two screws 24.
  • the piston position indicator 20 is furthermore extending a distance into the end cover 5 and through the end cover 4.
  • the core 22 of the piston position indicator 20 reciprocates only within an area corresponding to the distance A and cannot at all move into the extreme areas of the piston position indicator 20.
  • the best possible measuring accuracy is obtained for the inductive position indicator 20 as it is generally known that the most accurate measuring length of these position indicators is approx. the center 70% of the measuring length. Outside this length the linearity between the signal transmitted and the distance measured can decrease considerably.
  • the hydraulic cylinder 1 according to the invention can in a particularly advantageous manner be incorporated in painting robots, welding robots, other corresponding types of processing or tool machinery, or machinery as such carrying out a preprogrammed movement sequence.
  • Many of these applications imply that the piston 6 of the cylinder constantly moves various distances out of and back to the bottom position.
  • An obvious advantage is therefore obtained by the inductance sensor 15 transmitting altered electric signals, said signals being used for calibrating the measuring length of the inductive position indicator 20 each time the piston 6 returns to the bottom position.
  • the desired movement sequence can be preprogrammed in the signal processing equipment, such as the microcomputer, which thereby transmits signals to further equipment, such as the hydraulic equipment, allowing the hydraulic oil to flow to the gate 11 when the piston 6 is in its bottom position, and reversingly hydraulic oil to flow to the gate 10 when the piston 6 has moved an arbitrary predetermined distance corresponding to the electric signal received from the inductive position indicator 20.
  • the signal processing equipment such as the microcomputer
  • the hydraulic cylinder 1 according to the invention is neither of larger outer dimensions nor is made of other or stronger materials than a conventional hydraulic cylinder comprising neither built-in piston position indicators nor inductive sensors. As a result the cylinder is simultaneously inexpensive, quick, and easy to manufacture.
  • the inductive position indicator be connected to the housing of the hydraulic cylinder
  • the housing of the piston position indicator may be connected to the piston of the hydraulic cylinder.
  • the electric position indicators to show predetermined piston positions may for instances be built into the cylinder or situated outside thereof on other locations than at the end covers.

Landscapes

  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Fluid Mechanics (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Measurement Of Length, Angles, Or The Like Using Electric Or Magnetic Means (AREA)
  • Actuator (AREA)
EP19880902110 1987-02-20 1988-02-11 A hydraulic cylinder with a built-in electric piston position indicator Expired EP0306507B1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AT88902110T ATE65302T1 (de) 1987-02-20 1988-02-11 Hydraulischer zylinder mit eingebautem elektrischen anzeiger fuer die position des kolbens.

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DK886/87 1987-02-20
DK88687A DK165562C (da) 1987-02-20 1987-02-20 Hydraulisk cylinder med indbygget induktiv stempelpositionsgiver.

Publications (2)

Publication Number Publication Date
EP0306507A1 EP0306507A1 (en) 1989-03-15
EP0306507B1 true EP0306507B1 (en) 1991-07-17

Family

ID=8098640

Family Applications (1)

Application Number Title Priority Date Filing Date
EP19880902110 Expired EP0306507B1 (en) 1987-02-20 1988-02-11 A hydraulic cylinder with a built-in electric piston position indicator

Country Status (7)

Country Link
EP (1) EP0306507B1 (fi)
JP (1) JPH01502298A (fi)
AU (1) AU1393088A (fi)
BR (1) BR8805634A (fi)
DK (1) DK165562C (fi)
FI (1) FI884853A (fi)
WO (1) WO1988006243A1 (fi)

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR20160007912A (ko) 2014-07-10 2016-01-21 주식회사 세나코 선박용 연료펌프 플런저 및 배기밸브 제어 시스템
CN109578363B (zh) * 2018-12-14 2020-10-27 中国航空工业集团公司金城南京机电液压工程研究中心 一种活塞杆内置位移传感器的柔性固定约束结构

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1299432B (de) * 1967-12-30 1969-07-17 Maurer Ludwig Verfahren und Vorrichtung zur Stellwegmessung bei einer mit einem Druckmedium beaufschlagten Kolben-zylinder-Einheit
IT7829915A0 (it) * 1977-12-29 1978-11-17 Metacon Ag Apparato per il comando di sistemi azionatori idraulici a cilindro ed a pistone.
CA1196708A (en) * 1982-05-10 1985-11-12 Eugenio Espiritu Santo Position sensing cylinder
ES8502782A1 (es) * 1983-09-24 1985-01-16 Boge Gmbh Dispositivo para determinar el recorrido de un piston de grupos hidraulicos, neumaticos o hidroneumaticos

Also Published As

Publication number Publication date
JPH01502298A (ja) 1989-08-10
EP0306507A1 (en) 1989-03-15
FI884853A0 (fi) 1988-10-20
FI884853A (fi) 1988-10-20
DK165562C (da) 1993-04-26
DK88687D0 (da) 1987-02-20
DK165562B (da) 1992-12-14
DK88687A (da) 1988-08-21
BR8805634A (pt) 1989-08-15
WO1988006243A1 (en) 1988-08-25
AU1393088A (en) 1988-09-14

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