EP0258279B1 - Ram cylinder with an electric sensor for the end position of the piston - Google Patents

Ram cylinder with an electric sensor for the end position of the piston Download PDF

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Publication number
EP0258279B1
EP0258279B1 EP87900648A EP87900648A EP0258279B1 EP 0258279 B1 EP0258279 B1 EP 0258279B1 EP 87900648 A EP87900648 A EP 87900648A EP 87900648 A EP87900648 A EP 87900648A EP 0258279 B1 EP0258279 B1 EP 0258279B1
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EP
European Patent Office
Prior art keywords
piston
cylinder
end wall
working cylinder
force
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Expired
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EP87900648A
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German (de)
French (fr)
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EP0258279A1 (en
Inventor
Gerhard BRÜGGEN
Manfred Gaugler
Dieter Karr
Josef Winkler
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OFFERTA DI LICENZA AL PUBBLICO
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Robert Bosch GmbH
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • 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
    • F15B15/26—Locking mechanisms
    • 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

Definitions

  • the invention relates to a working cylinder according to the preamble of claim 1.
  • Arrangements of this type are already known. They are designed as single- or double-acting cylinders, the pistons of which can be acted upon by liquids or gases, in particular compressed air.
  • the inlet and the outlet of the pressure medium are controlled in such a way that when the piston reaches the stroke end position, the previous inlet closes and the outlet opens.
  • Various possibilities are known for measuring and determining the position of the piston of a working cylinder, in particular the reaching of the piston end position.
  • a working cylinder which has become known from DE-C-3014 331 uses a diaphragm made of stainless steel, welded to the cylinder end wall, as the end position switch, with which an actuating body carried by the piston is axially aligned. The deformation of the membrane is converted into a position signal via a sensor located outside the cylinder space.
  • DE-A-3221 574 is concerned with a cylinder with an integrated electrical signal transmitter, which in one embodiment has two insulated electrical conductors which are kept at different electrical potentials and which, in the stroke end position of the piston, touch the piston surface consisting of conductive material.
  • DE-A-2052 763 has also disclosed an electrical switching device, in particular serving as a limit switch, for converting the position of a mechanical sensor into an electrical signal, in which a piezoelectric crystal for triggering the switching process with the aid of the mechanical sensor changes the position on it is exposed to the pressure, the electrical signal generated at the crystal being used to control a device that effects the switching process.
  • the mechanical transmitter can be a component of the object to be controlled, for example the piston of a working cylinder.
  • the working cylinder according to the invention with the characterizing features of the main claim has the advantage that its piston can be reversed at any time after reaching the piston end position, regardless of the signal of the end position switch.
  • the piezoelectric transducer By applying a voltage to the piezoelectric transducer, the latter becomes an actuating element which overcomes a force holding the piston in its stroke end position and removes the piston from its position which seals the supply line of the pressure medium.
  • Such an actuator has no moving parts and is characterized by large travel ranges, short actuation times and large power transmission.
  • a common piezoelectric transducer is provided for detecting the piston end position and for lifting the piston off the cylinder end wall.
  • This transducer is expediently designed as a cylindrical body which is inserted into a bore in the cylinder end wall which extends in the direction of movement of the piston.
  • FIG. 1 An embodiment of the invention is shown in the drawing and explained in more detail in the following description with further advantages.
  • the figure shows a schematically represented working cylinder with the associated control devices in a longitudinal section.
  • the drawing shows a working cylinder 1 with a double-acting piston 2, which can be moved back and forth over a straight stroke, which can be reversed after reaching its end positions.
  • the cylinder 1 is closed on both sides by a cylinder cover 3 or 4 pressure-tight.
  • the cylinder covers are shown in one piece with the working cylinder 1 for the sake of clarity.
  • the piston 2 has a piston rod 5 which is guided to the outside through a bore in the cover 3 provided with a seal 6.
  • the pressure medium is supplied to the cylinder interior via lines 7 and 8 formed in the cylinder covers 3, 4.
  • the lines are formed in the region of the facing end walls of the cylinder covers as annular spaces 9 and 10, with which sealing rings 11 and 12 located on the end faces of the piston 2 cooperate.
  • return lines 13 and 14 are provided which open into the cylinder space near the end walls of the cylinder covers 3 and 4, respectively.
  • the lines contain a control slide 16 that can be actuated by an electromagnet 15. Depending on the position of this slide, either the feed line 8 and the drain line 14 or the feed line 7 and the drain line 13 are released.
  • the signal for switching the control slide 16 is generated by piston end position sensors which are arranged in or on the cylinder covers 3, 4 and are actuated by the piston 2 in the stroke end positions.
  • Piezoelectric transducers 17 and 18 serve as such end position transmitters.
  • these are designed as cylindrical hollow bodies, which are inserted into a centrally arranged bore 19 and 20 of the cover 3 and 4, respectively, which extends in the direction of movement of the piston. In the unloaded state, the hollow bodies protrude a few micrometers above the end wall of the lid.
  • the piston rod 5 passes through the hollow body 17.
  • Each transducer consists of several stacked piezoelectric perforated disks, which are arranged in an insulating housing. The disks are electrically connected in parallel. Every converter is connected to the electromagnet 15 via a line 21 or 22 which leads to the outside.
  • the piston 2 is held in its respective end stroke position by a force which is greater than the force of the pressure medium acting on the surface of the sealing rings 11 or 12 closing the annular space 9 or 10 of the feed lines 7 or 8.
  • this force is applied by permanent magnet rings 23, 24, which are fastened in one turn 25, 26 of the cylinder covers 3 and 4, respectively.
  • the end faces of the magnetic rings are flush with the end wall of the cylinder cover.
  • the magnetic rings 23, 24 are each opposed to a soft iron ring 27 or 28, which is anchored in the piston 2.
  • the converters 17, 18 can be alternately connected to voltage via the lines 21, 22.
  • the piezoelectric disks expand under the influence of the applied electric field and at the same time their diameters contract in the direction of the cylinder longitudinal axis, so that the piston 2 is lifted off the end wall of the cylinder cover.
  • the piston 2 is in its left stroke end position. It is fixed by the magnetic field of the ring magnet 24 on the end wall of the cylinder cover 4.
  • the pressure line 8 is opened so that the force of the pressure medium is applied to the sealing ring 12 of the piston 2. This force is less than the magnetic holding force.
  • the piezoelectric transducer 18 now receives an electrical voltage pulse via line 22, it expands and lifts piston 2 somewhat from the end wall of cylinder cover 4 while simultaneously opening sealing seat 10, 12.
  • the pressure of the pressure medium supplied through line 8 now acts on the entire piston surface, i. H. the hydraulic or pneumatic pressure is greater than the magnetic holding force.
  • the piston accordingly moves into the right stroke end position, the pressure medium on the right piston side being pressed out via the return line 13.
  • the return line Shortly before reaching the right end position, the return line is closed by the piston and the piston speed is slowed down somewhat.
  • the piezoelectric transducer 17 experiences a deformation.
  • the electrical signal generated thereby is given to the electromagnet 15 via the line 21 and an intermediate amplifier.
  • the trigger pulse for the movement of the piston 2 in the opposite direction can be input by applying an electrical voltage to the converter 17.
  • the changes in size of the piezoelectric transducers caused by the temperature can be compensated for by applying a direct voltage to the piezoceramic.
  • the superimposed alternating voltage signal which is generated by the compression of the converter when the piston strikes the end wall of one of the cylinder covers 3, 4, is used as the manipulated variable for the electromagnet 15.

Abstract

A ram cylinder (1, 3, 4) having an electric sensor for the end position of the piston is designed as a piezoelectric transformer (17 resp. 18). When voltage is applied to the piezoelectric transformer (17 resp. 18), the latter becomes an actuating element which overcomes a force that retains the piston (2) in its end-of-stroke position and drives the piston (2) away from the position where it seals the inlet passage (7 resp. 8) for the medium under pressure.

Description

Stand der TechnikState of the art

Die Erfindung geht aus von einem Arbeitszylinder nach dem Oberbegriff des Anspruchs 1. Anordnungen dieser Art sind bereits bekannt. Sie sind als einfach- oder doppelwirkende Zylinder ausgebildet, deren Kolben mit Flüssigkeiten oder Gasen, insbesondere Druckluft, beaufschlagbar sind. Der Einlass und der Auslass des Druckmediums wird hierbei so gesteuert, dass bei Erreichen der Hubendlage des Kolbens das Schliessen des bisherigen Einlasses und das Öffnen des Auslasses erfolgt. Es sind verschiedene Möglichkeiten bekannt, die Stellung des Kolbens eines Arbeitszylinders, insbesondere das Erreichen der Kolbenendstellung, zu messen und festzustellen. So verwendet beispielsweise ein durch die DE-C-3014 331 bekannt gewordener Arbeitszylinder als Endstellungsschalter eine mit der Zylinderstirnwand verschweisste Membrane aus Edelstahl, mit welcher ein vom Kolben getragener Betätigungskörper axial fluchtet. Die Verformung der Membran wird über einen ausserhalb desZylinderraumsangeordneten Fühler in ein Stellungssignal umgewandelt. Die DE-A-3221 574 befasst sich mit einem Zylinder mit integriertem elektrischen Signalgeber, welcher in einer Ausführungsform zwei isolierte elektrische Leiter aufweist, die auf unterschiedlichen elektrischen Potentialen gehalten werden und in der Hubendlage des Kolbens die aus leitendem Material bestehende Kolbenfläche berühren. Durch die DE-A-2052 763 ist ferner eine insbesondere als Endschalter dienende elektrische Schaltvorrichtung zur Umwandlung der Position eines mechanischen Gebers in ein elektrisches Signal bekannt geworden, bei welcher ein piezoelektrisches Kristall zur Auslösung des Schaltvorgangs mit Hilfe des mechanischen Gebers einer Änderung des auf ihn wirkenden Drucks ausgesetzt wird, wobei das am Kristall entstehende elektrische Signal zur Ansteuerung einer den Schaltvorgang bewirkenden Vorrichtung dient. Der mechanische Geber kann ein Bauteil des zu steuernden Objektes, beispielsweise der Kolben eines Arbeitszylinders, sein.The invention relates to a working cylinder according to the preamble of claim 1. Arrangements of this type are already known. They are designed as single- or double-acting cylinders, the pistons of which can be acted upon by liquids or gases, in particular compressed air. The inlet and the outlet of the pressure medium are controlled in such a way that when the piston reaches the stroke end position, the previous inlet closes and the outlet opens. Various possibilities are known for measuring and determining the position of the piston of a working cylinder, in particular the reaching of the piston end position. For example, a working cylinder which has become known from DE-C-3014 331 uses a diaphragm made of stainless steel, welded to the cylinder end wall, as the end position switch, with which an actuating body carried by the piston is axially aligned. The deformation of the membrane is converted into a position signal via a sensor located outside the cylinder space. DE-A-3221 574 is concerned with a cylinder with an integrated electrical signal transmitter, which in one embodiment has two insulated electrical conductors which are kept at different electrical potentials and which, in the stroke end position of the piston, touch the piston surface consisting of conductive material. DE-A-2052 763 has also disclosed an electrical switching device, in particular serving as a limit switch, for converting the position of a mechanical sensor into an electrical signal, in which a piezoelectric crystal for triggering the switching process with the aid of the mechanical sensor changes the position on it is exposed to the pressure, the electrical signal generated at the crystal being used to control a device that effects the switching process. The mechanical transmitter can be a component of the object to be controlled, for example the piston of a working cylinder.

Vorteile der ErfindungAdvantages of the invention

Der erfindungsgemässe Arbeitszylinder mit den kennzeichnenden Merkmalen des Hauptanspruchs hat demgegenüber den Vorteil, dass sein Kolben zu jedem beliebigen Zeitpunkt nach Erreichen der Kolbenendstellung, unabhängig vom Signal des Endstellungsschalters, umgesteuert werden kann. Durch Anlegen einer Spannung an den piezoelektrischen Wandler wird dieser zu einem Stellelement, das eine den Kolben in seiner Hubendlage haltende Kraft überwindet und den Kolben aus seiner die Zuleitung des Druckmediums abdichtenden Stellung entfernt. Ein solches Stellelement hat keine beweglichen Teile und zeichnet sich durch grosse Stellwege, kurze Stellzeiten und grosse Kraftübertragung aus. Zum Erfassen der Kolbenendstellung und zum Abheben des Kolbens von der Zylinderstirnwand ist nach einer vorteilhaften Ausführungsform der Erfindung ein gemeinsamer piezoelektrischer Wandler vorgesehen. Dieser Wandler ist zweckmässig als zylindrischer Körper ausgebildet, welcher in eine in Bewegungsrichtung des Kolbens verlaufende Bohrung der Zylinderstirnwand eingesetzt ist.The working cylinder according to the invention with the characterizing features of the main claim has the advantage that its piston can be reversed at any time after reaching the piston end position, regardless of the signal of the end position switch. By applying a voltage to the piezoelectric transducer, the latter becomes an actuating element which overcomes a force holding the piston in its stroke end position and removes the piston from its position which seals the supply line of the pressure medium. Such an actuator has no moving parts and is characterized by large travel ranges, short actuation times and large power transmission. According to an advantageous embodiment of the invention, a common piezoelectric transducer is provided for detecting the piston end position and for lifting the piston off the cylinder end wall. This transducer is expediently designed as a cylindrical body which is inserted into a bore in the cylinder end wall which extends in the direction of movement of the piston.

Zeichnungdrawing

Ein Ausführungsbeispiel der Erfindung ist in der Zeichnung dargestellt und in der nachfolgenden Beschreibung unter Angabe weiterer Vorteile näher erläutert. Die Figur zeigt einen schematisch dargestellten Arbeitszylinder mit den zugehörigen Steuereinrichtungen in einem Längsschnitt.An embodiment of the invention is shown in the drawing and explained in more detail in the following description with further advantages. The figure shows a schematically represented working cylinder with the associated control devices in a longitudinal section.

Beschreibung des AusführungsbeispielsDescription of the embodiment

Die Zeichnung zeigt einen Arbeitszylinder 1 mit einem doppelseitig beaufschlagten, über eine geradlinige Hubstrecke hin- und herbewegbaren Kolben 2, der jeweils nach Erreichen seiner Endstellungen umgesteuert werden kann. Der Zylinder 1 ist beidseitig durch je einen Zylinderdeckel 3 bzw. 4 druckdicht verschlossen. Die Zylinderdekkel sind der Übersichtlichkeit wegen einstückig mit dem Arbeitszylinder 1 dargestellt. Der Kolben 2 hat eine Kolbenstange 5, welche durch eine mit einer Dichtung 6 versehene Bohrung im Deckel 3 nach aussen geführt ist.The drawing shows a working cylinder 1 with a double-acting piston 2, which can be moved back and forth over a straight stroke, which can be reversed after reaching its end positions. The cylinder 1 is closed on both sides by a cylinder cover 3 or 4 pressure-tight. The cylinder covers are shown in one piece with the working cylinder 1 for the sake of clarity. The piston 2 has a piston rod 5 which is guided to the outside through a bore in the cover 3 provided with a seal 6.

Das Druckmittel wird dem Zylinderinnenraum über in den Zylinderdeckeln 3,4 ausgebildete Leitungen 7 bzw. 8 zugeführt. Die Leitungen sind im Bereich der einander zugekehrten Stirnwände der Zylinderdeckel als Ringräume 9 bzw. 10 ausgebildet, mit denen an den Stirnflächen des Kolbens 2 befindliche Dichtringe 11 bzw. 12 zusammenarbeiten. Zum Abführen des im Zylinder befindlichen Druckmediums sind Rücklaufleitungen 13 und 14 vorgesehen, die nahe der Stirnwände der Zylinderdeckel 3 bzw. 4 in den Zylinderraum münden. Die Leitungen enthalten einen durch einen Elektromagneten 15 betätigbaren Steuerschieber 16. Je nach Stellung dieses Schiebers werden entweder die Zuleitung 8 und die Abflussleitung 14 oder die Zuleitung 7 und die Abflussleitung 13 freigegeben.The pressure medium is supplied to the cylinder interior via lines 7 and 8 formed in the cylinder covers 3, 4. The lines are formed in the region of the facing end walls of the cylinder covers as annular spaces 9 and 10, with which sealing rings 11 and 12 located on the end faces of the piston 2 cooperate. To discharge the pressure medium located in the cylinder, return lines 13 and 14 are provided which open into the cylinder space near the end walls of the cylinder covers 3 and 4, respectively. The lines contain a control slide 16 that can be actuated by an electromagnet 15. Depending on the position of this slide, either the feed line 8 and the drain line 14 or the feed line 7 and the drain line 13 are released.

Das Signal für das Umschalten des Steuerschiebers 16 wird durch Kolbenendstellungsgeber erzeugt, welche in bzw. an den Zylinderdeckeln 3, 4 angeordnet sind und in den Hubendlagen durch den Kolben 2 betätigt werden. Als solche Endstellungsgeber dienen piezoelektrische Wandler 17 und 18. Diese sind im Ausführungsbeispiel als zylindrische Hohlkörper ausgebildet, welche in je eine zentrisch angeordnete und in Bewegungsrichtung des Kolbens verlaufende Bohrung 19 bzw. 20 des Deckels 3 bzw. 4 eingesetzt sind. Die Hohlkörper stehen im unbelasteten Zustand um einige Mikrometer über die Stirnwand der Deckel vor. Der Hohlkörper 17 wird von der Kolbenstange 5 durchgriffen. Jeder Wandler besteht aus mehreren, aufeinandergeschichteten piezoelektrischen Lochscheiben, die in einem lsolierstoffgehäuse angeordnet sind. Die Scheiben sind elektrisch parallel geschaltet. Jeder Wandler ist über eine nach aussen geführte Leitung 21 bzw. 22 mit dem Elektromagneten 15 verbunden.The signal for switching the control slide 16 is generated by piston end position sensors which are arranged in or on the cylinder covers 3, 4 and are actuated by the piston 2 in the stroke end positions. Piezoelectric transducers 17 and 18 serve as such end position transmitters. In the exemplary embodiment, these are designed as cylindrical hollow bodies, which are inserted into a centrally arranged bore 19 and 20 of the cover 3 and 4, respectively, which extends in the direction of movement of the piston. In the unloaded state, the hollow bodies protrude a few micrometers above the end wall of the lid. The piston rod 5 passes through the hollow body 17. Each transducer consists of several stacked piezoelectric perforated disks, which are arranged in an insulating housing. The disks are electrically connected in parallel. Every converter is connected to the electromagnet 15 via a line 21 or 22 which leads to the outside.

Der Kolben 2 wird durch eine Kraft in seiner jeweiligen Endhublage gehalten, die grösser ist als die auf die Fläche der den Ringraum 9 bzw. 10 der Zuleitungen 7 bzw. 8 verschliessenden Dichtringe 11 bzw. 12 einwirkende Kraft des Druckmediums. Diese Kraft wird im Ausführungsbeispiel durch Permanentmagnetringe 23, 24 aufgebracht, die in je einer Ausdrehung 25, 26 der Zylinderdekkel 3 bzw. 4 befestigt sind. Die Stirnflächen der Magnetringe schliessen mit der Stirnwand der Zylinderdeckel bündig ab. Den Magnetringen 23, 24 stehtje ein Weicheisenring 27 bzw. 28 gegenüber, welcher im Kolben 2 verankert ist. Über die Leitungen 21, 22 können die Wandler 17, 18 wechselweise an Spannung gelegt werden. Dabei dehnen sich die piezoelektrischen Scheiben unter dem Einfluss des angelegten elektrischen Feldes bei gleichzeitiger Kontraktion ihrer Durchmesser in Richtung der Zylinder-Längsachse aus, so dass der Kolben 2 von der Stirnwand des Zylinderdekkels abgehoben wird. Um die Masse des Kolbens 2 möglichst klein zu halten, ist es vorteilhaft, den Kolben aus einem Kunststoff anzufertigen, in den die beiden Weicheisenringe 27, 28 eingebettet sind. Möglich ist auch eine Ausführung, bei welcher die Dauermagnete im Kolben 2 fixiert sind und die Zylinderdeckel aus Weicheisen bestehen.The piston 2 is held in its respective end stroke position by a force which is greater than the force of the pressure medium acting on the surface of the sealing rings 11 or 12 closing the annular space 9 or 10 of the feed lines 7 or 8. In the exemplary embodiment, this force is applied by permanent magnet rings 23, 24, which are fastened in one turn 25, 26 of the cylinder covers 3 and 4, respectively. The end faces of the magnetic rings are flush with the end wall of the cylinder cover. The magnetic rings 23, 24 are each opposed to a soft iron ring 27 or 28, which is anchored in the piston 2. The converters 17, 18 can be alternately connected to voltage via the lines 21, 22. The piezoelectric disks expand under the influence of the applied electric field and at the same time their diameters contract in the direction of the cylinder longitudinal axis, so that the piston 2 is lifted off the end wall of the cylinder cover. In order to keep the mass of the piston 2 as small as possible, it is advantageous to manufacture the piston from a plastic in which the two soft iron rings 27, 28 are embedded. An embodiment is also possible in which the permanent magnets are fixed in the piston 2 and the cylinder covers are made of soft iron.

Die Arbeitsweise der vorstehend beschriebenen Zylinderanordnung ist wie folgt:The operation of the cylinder arrangement described above is as follows:

In der Zeichnung befindet sich der Kolben 2 in seiner linken Hubendlage. Er wird durch das Magnetfeld des Ringmagneten 24 an der Stirnwand des Zylinderdeckels 4 festgelialten. Die Druckleitung 8 ist geöffnet, so dass die Kraft des Druckmediums am Dichtring 12 des Kolbens 2 anliegt. Diese Kraft ist kleiner als die magnetische Haltekraft. Erhält nun der piezoelektrische Wandler 18 über die Leitung 22 einen elektrischen Spannungsimpuls, so dehnt er sich aus und hebt den Kolben 2 unter gleichzeitigem Öffnen des Abdichtsitzes 10, 12 etwas von der Stirnwand des Zylinderdeckels 4 ab. Der Druck des durch die Leitung 8 zugeführten Druckmediums wirkt nun auf die gesamte Kolbenfläche, d. h. der Hydraulik- bzw. Pneumatikdruck wird grösser als die magnetische Haltekraft. Der Kolben bewegt sich demzufolge in die rechte Hubendlage, wobei das Druckmedium auf der rechten Kolbenseite über die Rücklaufleitung 13 ausgepresstwird. Kurz vor Erreichen der rechten Endlage wird die Rücklaufleitung durch den Kolben geschlossen und die Kolbengeschwindigkeit etwas abgebremst. Beim Auftreffen des Kolbens auf die Stirnwand des Zylinderdeckels 3 erfährt der piezoelektrische Wandler 17 eine Deformation. Das dadurch erzeugte elektrische Signal wird über die Leitung 21 und einen zwischengeschalteten Verstärker auf den Elektromagneten 15 gegeben. Dieser überführt den Steuerschieber 16 in seine andere Endlage, in welcher die Rücklaufleitung 14 und die Druckleitung 7 geöffnet, die Leitungen 8 und 13 hingegen geschlossen sind. Danach kann durch Anlegen einer elektrischen Spannung an den Wandler 17 der Auslöseimpuls für die Bewegung des Kolbens 2 in umgekehrter Richtung eingegeben werden.In the drawing, the piston 2 is in its left stroke end position. It is fixed by the magnetic field of the ring magnet 24 on the end wall of the cylinder cover 4. The pressure line 8 is opened so that the force of the pressure medium is applied to the sealing ring 12 of the piston 2. This force is less than the magnetic holding force. If the piezoelectric transducer 18 now receives an electrical voltage pulse via line 22, it expands and lifts piston 2 somewhat from the end wall of cylinder cover 4 while simultaneously opening sealing seat 10, 12. The pressure of the pressure medium supplied through line 8 now acts on the entire piston surface, i. H. the hydraulic or pneumatic pressure is greater than the magnetic holding force. The piston accordingly moves into the right stroke end position, the pressure medium on the right piston side being pressed out via the return line 13. Shortly before reaching the right end position, the return line is closed by the piston and the piston speed is slowed down somewhat. When the piston strikes the end wall of the cylinder cover 3, the piezoelectric transducer 17 experiences a deformation. The electrical signal generated thereby is given to the electromagnet 15 via the line 21 and an intermediate amplifier. This transfers the control slide 16 into its other end position, in which the return line 14 and the pressure line 7 are open, but the lines 8 and 13 are closed. Thereafter, the trigger pulse for the movement of the piston 2 in the opposite direction can be input by applying an electrical voltage to the converter 17.

Der Einflusstemperaturbedingter Grössenänderungen der piezoelektrischen Wandler lässt sich durch Anlegen einer Gleichspannung an die Piezokeramik kompensieren. Als Stellgrösse für den Elektromagneten 15 wird das überlagerte Wechselspannungssignal verwertet, das durch die Kompression des Wandlers beim Auftreffen des Kolbens auf die Stirnwand eines der Zylinderdeckel 3, 4 erzeugt wird.The changes in size of the piezoelectric transducers caused by the temperature can be compensated for by applying a direct voltage to the piezoceramic. The superimposed alternating voltage signal, which is generated by the compression of the converter when the piston strikes the end wall of one of the cylinder covers 3, 4, is used as the manipulated variable for the electromagnet 15.

Claims (7)

1. Working cylinder (1) with an electrical end position switch (17,18), which is attached to the cylinder cover (3,4) and is actuated in the end-of-stroke position by the piston (2), characterized in that the supply duct (7 or 8) for a pressure medium acting on the piston (2) enters at the cylinder end wall, which supply duct is closed in the end-of-stroke position by a part (11 or 12) of the end surface of the piston, that the piston is held by a force in its end-of-stroke position, which force is larger than the force of the pressure medium acting on the partial surface of the piston, and that a piezoelectric transducer (17 or 18) which can be connected to a potential source is located in the cylinder end wall, which transducer expands in the displacement direction of the piston and lifts its end surface from the cylinder end wall after the application of the potential.
2. Working cylinder according to Claim 1, characterized in that a joint piezoelectric transducer (17 or 18) is provided for sensing the piston end position and for raising the piston (2) from the cylinder end wall.
3. Working cylinder according to Claim 1 or 2, characterized in that the piezoelectric transducer (17 or 18) is designed as a cylindrical body which is inserted in a hole (19 or 20) of the cylinder end wall extending in the direction of motion of the piston (2).
4. Working cylinder according to Claim 3, characterized in that the piezoelectric transducer (17) is designed as a centrally located hollow cylinder which is penetrated by a piston rod (5).
5. Working cylinder according to one of the preceding claims, characterized in that the force holding the piston (2) in its end-of-stroke position is applied by a permanent magnet (23 or 24).
6. Working cylinder according to Claim 5, characterized in that the permanent magnet (23 or 24) is fastened in the cylinder (1) and forms a part of the cylinder end wall.
7. Working cylinder according to Claim 6, characterized in that the piston (2) consists of a plastic body with soft iron inserts (27, 28).
EP87900648A 1986-02-08 1987-01-14 Ram cylinder with an electric sensor for the end position of the piston Expired EP0258279B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE19863603992 DE3603992A1 (en) 1986-02-08 1986-02-08 WORKING CYLINDER WITH AN ELECTRIC PISTON ENCODER
DE3603992 1986-02-08

Publications (2)

Publication Number Publication Date
EP0258279A1 EP0258279A1 (en) 1988-03-09
EP0258279B1 true EP0258279B1 (en) 1989-09-27

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EP87900648A Expired EP0258279B1 (en) 1986-02-08 1987-01-14 Ram cylinder with an electric sensor for the end position of the piston

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US (1) US4843951A (en)
EP (1) EP0258279B1 (en)
JP (1) JPH0776563B2 (en)
DE (2) DE3603992A1 (en)
WO (1) WO1987004763A1 (en)

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Also Published As

Publication number Publication date
WO1987004763A1 (en) 1987-08-13
DE3603992A1 (en) 1987-08-20
DE3760634D1 (en) 1989-11-02
JPH0776563B2 (en) 1995-08-16
US4843951A (en) 1989-07-04
JPS63502296A (en) 1988-09-01
EP0258279A1 (en) 1988-03-09

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