EP3129661B1 - Method for sensing position or movement of a piston in a cylinder - Google Patents

Description

The invention relates to a method for detecting the position and / or movement of a piston in a cylinder having a longitudinal center axis, wherein a liquid is present on a first piston side and a gas on a second piston side.

Further, the invention relates to a cylinder assembly having a cylinder and having a movable therein along a longitudinal center axis of the cylinder piston, which is adapted to separate on a first piston side pending liquid from a pending on a second side of the piston gas.

Such a method and such a cylinder arrangement are used in particular in connection with piston accumulators. In these, the liquid is a hydraulic fluid that is pressed against a gas (for example, nitrogen) in this memory. The liquid-side cylinder volume communicates regularly via a hydraulic connection with a hydraulic device, from which hydraulic fluid can flow into the cylinder while overcoming the gas pressure prevailing on the second piston side or, upon release of the pressure, can flow out of the cylinder into the hydraulic device by displacement of the piston.

On the side facing the second piston side, the cylinder regularly has a connection via which gas with the desired pressure can be supplied to the cylinder. After reaching the desired gas pressure, the connection can be clamped. In order to increase the storage volume, a constant contact with a larger, external gas pressure source can be maintained, which also - depending on the volume ratios between the cylinder and the gas pressure source - kept the gas pressure independent of the position of the piston in the cylinder more or less constant can be.

For the functionality of such a piston accumulator, it is important at which position the piston is located in the cylinder. Thus, for example, a maintenance of a hydraulic pressure to be effected with the aid of the piston accumulator in the hydraulic device is possible only as long as the first piston side is not in abutment with a cap delimiting the liquid volume of the cylinder. On the other hand, the hydraulic pressure in the hydraulic device with the help of the piston accumulator can only be limited so long as the second piston side does not abut against a lid bounding the gas volume of the cylinder. It is already desirable in this respect knowledge of the current piston position to maintain the reliability of a piston accumulator comprehensive device desirable.

In addition, it may be necessary to detect changes in the operating state of a piston accumulator device, in particular the hydraulic device, to detect changes in position of the piston. These may indicate, for example, a pressure drop due to a leak or a pressure increase due to load peaks.

• Die Position des Kolbens wird mit einem Seilzugmesssystem erfasst. Das eine Ende des Seils ist an einer Rolle, die mit einer Feder vorgespannt ist, das andere Ende des Seils an dem Kolbenboden befestigt. Die Bewegung des Kolbens wird über ein an der Rolle vorgesehenes Drehpotentiometer erfasst.
• Das eine Ende eines Seils ist wiederum an dem Kolben befestigt. Das andere, aus dem Zylinder herausgeführte Ende des Seils trägt einen in einem Rohr geführten Permanentmagneten, welcher an dem Rohr angebrachte, magnetosensitive Mittel in Abhängigkeit seiner Position aktiviert und somit die Kolbenbewegung und -position erkennbar macht.
• Erfassung der Kolbenposition mittels Ultraschall, indem außerhalb des Zylinders eine oder mehrere Ultraschallsende/Empfangseinheiten vorgesehen sind. Jede dieser Einheiten erkennt den Übergang zwischen Kolben und Öl, so dass eine Kolbenbewegung und -position mit einer Genauigkeit erfassbar ist, die vom Abstand der Ultraschallsende/Empfangseinheiten abhängt.
• Erfassung der Position- und/oder der Bewegung des Kolbens mit Hilfe einer aus dem Zylinder herausgeführten Kolbenstange und mit dieser zusammen wirkendem Wegaufnehmer.
• Flüssigkeitsseitig angeordnetes Ultraschallwegmesssystem, welches den Abstand zwischen dem flüssigkeitsseitigen Deckel des Zylinders und dem Kolben erfasst.

For position and / or motion detection of a piston of a piston accumulator, the following systems are known, for example, from Hydac International GmbH, Sulzbach, Germany:

• The position of the piston is detected by a cable measuring system. One end of the rope is secured to a roller biased by a spring, the other end of the rope to the piston bottom. The movement of the piston is detected by a rotary potentiometer provided on the roller.
• The one end of a rope is in turn attached to the piston. The other, led out of the cylinder end of the rope carries a guided in a tube permanent magnet which activates attached to the tube, magneto-sensitive means depending on its position and thus makes the piston movement and position recognizable.
• Detecting the position of the piston by means of ultrasound, by providing one or more ultrasonic transmitting / receiving units outside the cylinder. Each of these units detects the transition between the piston and the oil, so that a piston movement and position can be detected with an accuracy that depends on the distance of the ultrasonic transmitter / receiver units.
• Detecting the position and / or the movement of the piston by means of a guided out of the cylinder piston rod and with this cooperating transducer.
• Ultraschallwegig arranged Ultraschallwegmesssystem which detects the distance between the liquid-side lid of the cylinder and the piston.

A disadvantage of these systems is that they either require the removal of components from the cylinder, which requires expensive sealing arrangements which are subject to wear. With other systems, position and / or motion detection can only be achieved with limited accuracy or require the presence of hydraulic fluid for coupling.

From the US 2002/083826 A1 For example, a hydraulic actuator is known which has a cylinder with a piston moved by means of a hydraulic fluid. To determine the position of the piston, a laser beam is directed by means of a light guide in the cylinder on the piston, reflected at this and fed by means of a light guide to a control unit with which the light transit time is measured.

The invention is therefore based on the object to provide an improved method for detecting the position and / or movement of a piston, in particular a piston accumulator, and an improved cylinder assembly with a cylinder and with a movable along a longitudinal central axis of the cylinder piston, in particular a piston accumulator ,

This object is achieved by the reproduced in claim 1 method and by the reproduced in claim 3 cylinder arrangement.

In the method according to the invention, a beam of an almost monochromatic wave is directed onto the second side of the bulb at an angle deviating from 90.degree. And reflected by the latter, and the location of the impact of the reflected beam is detected. Due to the angle of incidence, which may vary, for example, between 0.5 and 10 ° from a right angle, a piston movement is reliably detected by changing the location of the impact of the reflected beam.

A particular advantage of the method according to the invention is that it does not require a sealing arrangement for sealing moving parts, such as piston rods or ropes. It is also advantageous that the method is applicable to the gas side of the piston. Thus, there is the possibility of creating a redudant operating system in which on the liquid side, for example, one of the aforementioned, belonging to the prior art systems for position and / or movement detection of the piston is used. In particular, the application of the ultrasonic path measuring system may be mentioned here.

The used beam of a nearly monochromatic wave may be a laser beam.

In operation, if there is a possibility that the pressure of the gas on the second piston side changes, which is the case, for example, when the cylinder volume does not communicate with a relatively large gas volume of constant pressure, the pressure on the second piston side becomes detected gas. Because a change in density associated with a gas pressure change leads to a change in the optical properties of the gas, in particular the change in the optical refractive index between the gas and a possibly before a sensor for detecting the reflected beam shield, whereby the place of impact of the reflected beam at the same position the piston would be changed. By detecting the pressure of the gas present on the second piston side, this effect can be taken into account in the piston position and / or motion detection.

A change in the temperature of the gas present on the second piston side can also result in a change in the optical properties with the effects described in connection with a pressure change. Accordingly, alternatively or additionally, the temperature of the gas present on the second piston side is detected and the effects are taken into account with a suitable routine in the position and / or motion detection.

The cylinder arrangement according to the invention, which is preferably used to form a piston accumulator, comprises a radiation source, by means of which an applied beam of a nearly monochromatic wave can be directed onto the second piston side at an angle deviating from 90 °. In order that the reflection of the beam on the second piston side takes place with as little scattering as possible, a reflection device, for example a mirror, is provided on the latter. If the mirror is aligned perpendicular to the longitudinal central axis of the cylinder, the radiation source is preferably designed such that the emitted beam is aligned at an acute angle to the direction of the longitudinal central axis, preferably between 0.5 ° and 10 °. The cylinder arrangement further comprises a detection device, by means of which the location of the impact of the reflected beam can be detected.

The radiation source and the detection device may in particular be provided on one, the cylinder volume on the lid bounding the second piston side.

The radiation source is preferably a laser source.

The detection device preferably comprises an area sensor, which - particularly preferably - with respect to its sensitivity to the properties of the monochromatic wave, in particular the wavelength and the intensity of the reflected beam, is tuned.

In order to be able to take into account the influence of a possible gas pressure change on the position and / or movement detection, a gas pressure detection device is provided.

In order to be able to take into account corresponding effects of a possible temperature change of the gas present at the second piston side, a temperature detection device is alternatively or additionally provided.

The cylinder arrangement according to the invention comprises an evaluation device for taking into account the influence of the pressure and / or the temperature on the location of the impact of the reflected beam in the position and / or movement detection of the piston, which comprises corresponding correction routines. These correction routines may include correction functions that are computationally and / or empirically determined and take into account the influence of a pressure and / or temperature change on the location of the impact of the reflected beam at a specific position of the piston.

In a particularly preferred embodiment of the cylinder arrangement according to the invention is a further device for position and / or movement detection the piston is provided, which detects in particular electrically, electromagnetically, acoustically and / or mechanically the piston position and / or movement. This second device may be an initially described, belonging to the prior art.

Fig. 1

ein Blockschaltbild dieses Ausführungsbeispiels bei längsgeschnittenem Zylinder;

Fig. 2

einen Längsschnitt durch den Zylinder mit dem Kolben in einer ersten Position;

Fig. 3

eine Fig. 2 entsprechende Ansicht mit dem Kolben in einer zweiten Position;

Fig. 4

den Ausschnitt IV in Fig. 2;

Fig. 5

den Ausschnitt V in Fig. 3 sowie

Fig. 6

den Ausschnitt VI in Fig. 3 in perspektivischem Längsschnitt.

The invention will be explained below with reference to the accompanying drawings, which schematically illustrate an embodiment of the invention. Show it:

Fig. 1

a block diagram of this embodiment with a longitudinally cut cylinder;

Fig. 2

a longitudinal section through the cylinder with the piston in a first position;

Fig. 3

a Fig. 2 corresponding view with the piston in a second position;

Fig. 4

the section IV in Fig. 2 ;

Fig. 5

the section V in Fig. 3 such as

Fig. 6

the detail VI in Fig. 3 in perspective longitudinal section.

The embodiment of a cylinder arrangement shown in the drawing comprises a cylinder 1 with a longitudinal center axis L. In the cylinder, a piston 2 is provided, which is displaceable along the longitudinal central axis L. The piston comprises sealing means not shown in the drawing in a conventional manner, such as piston rings, to effect a sealing effect between an outer periphery and the inner periphery of the cylinder 1.

On the right side in the drawing, the piston has a recess 3, whereas the side of the piston shown on the left in the drawing just trained. The side shown on the left in the drawing forms a first piston side 4, to which a liquid, for example an oil or a water-glycol mixture, is present during operation of the cylinder arrangement as piston accumulator. The thus formed liquid volume 5 of the cylinder 1 is limited to the outside by a first cover 6. The latter has a central connection bore 7 for connecting a hydraulic device, not shown in the drawing.

In operation, the liquid volume 5 is regularly completely filled with liquid. In order to keep this liquid under pressure and to be able to compensate for changes in the liquid volume in the hydraulic device, a gas volume 10 is delimited between the second piston side 8 opposite the first piston side 4 and a second cover 9 and the cylinder 1. This is in the operation of the piston-cylinder assembly regularly with pressurized nitrogen, if it is the liquid is oil, or filled with air, when the liquid is water-glycol mixture.

In order to detect a position and / or movement of the piston 2 in the cylinder 1, on the second cover 9, an arrangement 11 comprising a radiation source 12, by means of which a beam of a nearly monochromatic wave on the second piston side 8 can be directed, and a detection device 13, by means of which the location of the impingement of the reflected beam can be detected, arranged. The detection direction may include an area sensor.

Further, on the second lid 9, a gas pressure detecting means 14 and a temperature detecting means 15 are provided which detect the pressure and the temperature of the gas in the gas volume 10 located. The arrangement 11 is electrically connected to a device 16 for driving the radiation source 12 and for reading the detection device 13. The gas pressure detection device 14 is electrically connected to a signal converter 17, the temperature detection device 15 to a signal converter 18.

The device 16 and the signal converters 17 and 18, in turn, are electrically connected to a signal processing device 19 which, taking into account pressure and temperature correction functions from the signals obtained from the device 16 at a first output 20, the actual position of the piston 2 in the cylinder 1 and a second output 21 emits a signal which is generated at a movement of the piston 2 from a rest position.

The structural design of the illustrated embodiment and its operation will now be with reference to Fig. 2 to 6 further explained:
As in Fig. 2 can be seen, which shows the piston 2 in a displaced from the middle to the first cover 6 position, with the aid of the radiation source 12, a beam of a nearly monochromatic wave, here a laser beam 22 is emitted to the second piston side 8. As in Fig. 6 can be seen, the second piston side 8 is provided with a mirror 23 which is aligned at least almost perpendicular to the central longitudinal axis L. Since the load beam 22 impinges on the mirror 23 at an angle oblique to the direction of the longitudinal central axis L, the reflected beam 24 is reflected to the detection device 13 at a corresponding angle of departure of opposite sign.

As by comparison of FIGS. 2 and 3 When the piston 2 is displaced in the cylinder along the central longitudinal axis L, the point of incidence of the laser beam 22 shifts to the mirror 23, in the case of FIG FIGS. 2 and 3 illustrated embodiment at a displacement of the piston according to the drawing to the right upwards. Since the angle of incidence with respect to the central longitudinal axis L remains constant, the location of impingement P of the reflected beam 24 on the detection device 13 moves upward, so that by detecting the location of the impact P both the position of the piston 2 in the cylinder 1, and the beginning of a movement is detectable.

As in Fig. 6 2, the gas volume 10 is separated from the device 11 by a glass pane inserted from outside into a stepped bore 25. Between the step of the bore and the glass sheet is a seal 27 is inserted. Against this seal, the glass sheet is pressed by means of a threaded sleeve 28 which is screwed into a threaded bore 29.

LIST OF REFERENCE NUMBERS

1

cylinder

2

piston

3

deepening

4

first piston side

5

liquid volume

6

first lid

7

connection bore

8th

second piston side

9

second lid

10

gas volume

11

arrangement

12

radiation source

13

detector

14

Gas detector

15

Temperature sensing device

16

Facility

17

signal converter

18

signal converter

19

Signal processing device

20

first exit

21

second exit

22

laser beam

23

mirror

24

reflected beam

25

stepped bore

26

pane

27

poetry

28

threaded sleeve

29

threaded hole

L

Longitudinal central axis

P

Place of impact

Claims (6)

1. Method for detecting the position and/or movement of a piston (2) in a cylinder (1) that comprises a central longitudinal axis (L), a liquid being present on a first piston side (4) and a gas being present on a second piston side (8), a beam (22) of a near-monochromatic wave being emitted to the second piston side (8) in the direction of the central longitudinal axis (L) at an angle of incidence that is different from 90° and being reflected by said piston side, and the location of the impingement (P) of the reflected beam (24) being detected, characterized in that the pressure of the gas on the second piston side (8) is detected, and/or in that the temperature of the gas on the second piston side (8) is detected, and the influence of the gas pressure and/or of the temperature on the location of the impingement (P) of the reflected beam (24) is taken into account when the position and/or movement of the piston (2) is detected.
2. Method according to claim 1, characterized in that the beam (22) of a near-monochromatic wave is a laser beam.
3. Cylinder assembly comprising a cylinder (1) and comprising a piston (2) that is movable therein along the central longitudinal axis (L) of the cylinder (1), which assembly is suitable for separating a liquid on a first piston side (4) from a gas on a second piston side (8), the cylinder assembly comprising a radiation source (12) by means of which a beam (22) of a near-monochromatic wave can be directed towards the second piston side (8) at an angle that is different from 90°, and the second piston side (8) comprising a means for reflecting the beam, and the cylinder assembly comprising a detection means (13) by means of which the location of the impingement (P) of the reflected beam (24) can be detected, characterized in that a gas pressure detection means (14) is provided for detecting the gas pressure on the second piston side (8), and/or in that a temperature detection means (15) is provided for detecting the temperature of the gas on the second piston side (8), and in that an evaluation means is provided for taking into account the influence of the pressure and/or of the temperature on the location of the impingement (P) of the reflected beam (24) when the position and/or movement of the piston (2) is detected.
4. Cylinder assembly according to claim 3, characterized in that the radiation source (12) is a laser source.
5. Cylinder assembly according to either claim 3 or claim 4, characterized in that the detection means (13) comprises a surface sensor that is preferably adapted, with regard to its sensitivity, to the properties of the monochromatic wave.
6. Cylinder assembly according to any of claims 3 to 5, characterized in that a second means is provided for detecting the position and/or movement of the piston, which means detects the position and/or movement of the piston preferably electrically, electromagnetically, acoustically and/or mechanically.

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