Ultrasonic displacement measurement system and method for ultrasonic displacement measurement

Abstract

An ultrasonic displacement measurement system for hydraulic accumulators (3) has a movable separating element (5) separating two media chambers (9, 11) from each other in a media-tight manner within a housing (7). One media chamber (9) holds a compressible fluid or an incompressible fluid. The other media chamber (11) holds a compressible working gas. The particular position of the movable separating element (5) within the housing (7) can be detected by an ultrasonic sensor (13) that performs the position detection of the separating element (5) on the side of the media chamber (11) having the compressible fluid. A method for ultrasonic displacement measurement uses that system.

Claims

1. An ultrasonic displacement measuring system, comprising: a housing with first and second media chambers, said first media chamber having a compressible or incompressible fluid therein, said second media chamber having a compressible fluid therein; a separating element movably mounted in said housing and separating said first and second media chambers from one another; and a stationary ultrasonic sensor being in said housing and detecting positions of said separating element in said housing on a side of said separating element exposed in said second media chamber, said ultrasonic sensor being held in an inside of a sensor holder with a sensor chamber connected in fluid communication with said second media chamber through a media channel in said sensor holder and being exposed on opposite first and second sides thereof to equal pressures in said sensor chamber and in said second media chamber, respectively.

2. An ultrasonic displacement measuring system according to claim 1 wherein said compressible fluid in said second media chamber is a working gas.

3. An ultrasonic displacement measuring system according to claim 1 wherein said sensor chamber is separated from an environment outside said housing and said ultrasonic sensor by a glass part.

4. An ultrasonic displacement measuring system according to claim 3 wherein said glass part comprises a feedthrough mounting a cable connection from said ultrasonic sensor to a control unit.

5. An ultrasonic displacement measuring system according to claim 1 wherein said ultrasonic sensor is disposed stationary on a lid part of said housing such that a part of said sensor chamber with said media channel protrudes by a pre-determinable projection into said second media chamber; and in each position of said separating element, said separating element is maintained at a distance from said ultrasonic sensor.

6. An ultrasonic displacement measuring system according to claim 1 wherein said ultrasonic sensor comprises an ultrasonic transducer having a piezoceramic disc, said piezoceramic disc being disposed on a structure.

7. An ultrasonic displacement measuring system according to claim 6 wherein said structure seals an end of said sensor chamber in a direction of said second media chamber.

8. An ultrasonic displacement measuring system according to claim 6 wherein said sensor chamber is separated from an environment outside said housing and said ultrasonic sensor by a glass part; and said media channel is between said structure and said glass part.

9. An ultrasonic displacement measuring system according to claim 1 wherein a reference measuring section is present within said compressible fluid of said second media chamber and is delimited by first and second reference points, said first reference point being formed by said ultrasonic sensor, said second reference point being a reflection point.

10. An ultrasonic displacement measuring system according to claim 9 wherein said first and second reflection points are stationary relative to one another.

11. An ultrasonic displacement measuring system according to claim 10 wherein said second reference point has a shape of a boundary wall of said sensor chamber.

12. An ultrasonic displacement measuring system according to claim 1 wherein said separating element is a rigid limiting piston movable in said housing along a longitudinal axis of said housing, said ultrasonic sensor being arranged coaxial to said longitudinal axis.

13. An ultrasonic displacement measuring system according to claim 1 wherein said first media chamber has an incompressible fluid therein; and said separating element is a rigid limiting piston and comprises a collecting device for said incompressible fluid penetrating from said first media chamber through a gap between said limiting piston and said housing into said second media chamber during operation of the ultrasonic displacement measuring system, said collection device being adjacent and opposite said ultrasonic sensor in a direct sound-emitting direction thereof.

14. An ultrasonic displacement measuring system according to claim 13 wherein said collecting device comprises a reservoir in said limiting piston.

15. An ultrasonic displacement measuring system according to claim 1 wherein said ultrasonic sensor has an operating frequency between a low frequency having a small wave-dependent amplitude modulation occurring due to dispersion and a comparatively higher frequency permitting a higher resolution of displacement measurement at a lower wavelength.

16. An ultrasonic displacement measuring system according to claim 15 wherein said low frequency is 100 kHz; and said higher frequency is 150 kHz.

17. A method of ultrasonic displacement measurement using an ultrasonic displacement measuring system having a housing with first and second media chambers with a compressible or incompressible fluid and a compressible fluid therein, respectively, having a separating element movably mounted in the housing and separating the first and second media chambers from one another, having a stationary ultrasonic sensor being in the housing and detecting positions of the separating element in the housing on a side of the separating element exposed in the second media chamber with the ultrasonic sensor being held in an inside of a sensor holder with a sensor chamber connected in fluid communication with the second media chamber through a media channel in the ultrasonic sensor holder and being exposed on opposite first and second sides thereof to equal pressures in said sensor chamber and in said second media chamber, respectively, the method comprising steps of: emitting an acoustic signal by the ultrasonic sensor; detecting reverberations at the separating element and at a reference point opposite the ultrasonic sensor; determining a sound propagation velocity in the compressible fluid in the second media chamber from a propagation delay of the acoustic signal from the ultrasonic sensor to the reference point and back; and determining a distance of the separating element from the ultrasonic sensor from the sound propagation velocity and the propagation delay of the acoustic signal from the ultrasonic sensor to the separating element and back.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Referring to the drawings that form a part of this disclosure:

(2) FIG. 1 is a side view in section of a pressure accumulator having an ultrasonic displacement measuring system according to an exemplary embodiment of the invention; and

(3) FIG. 2 is an enlarged and partial side view in section of the ultrasonic sensor of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

(4) In FIG. 1, an ultrasonic displacement measuring system 1 is shown with a hydraulic accumulator 3 having at least one movable separating element 5, separating first and second media chambers 9, 11 from each other within a housing 7 in a largely media-tight manner. The first media chamber 9 receives an incompressible fluid, in particular in the form of hydraulic oil. The second media chamber 11 receives a compressible fluid, in particular in the form of a working gas, here nitrogen (N.sub.2). Another compressible fluid can be introduced in the first media chamber 9, for example, in the form of methane or inert gases. Other incompressible fluids, such as alcohols, or even pasty fluid media can be introduced in the first media chamber 9. The respective position of the movable separating element 5 inside the housing 7 can be detected by an ultrasonic sensor 13.

(5) In FIG. 1 the housing 7 has a tubular housing part 15, into which two end lid portions 17, 19 have been screwed via threaded sections 21. The lid parts 17, 19 are sealed by gaskets 25 retained in circumferential grooves 23 against the tubular housing part 15. The two lid parts 17, 19 have coaxial bores 27, 29, whereby the lid part 17, which leads to the first media chamber 9 having the incompressible fluid, has a terminal 31 for a fluid line (not shown in detail) of a hydraulic circuit.

(6) The separating element 5 is located between the lid parts 17, 19. The separating element 5 is formed of a rigid limitation piston arranged movably in the direction of its longitudinal axis LA within the housing 7. The limiting piston 5 has a shaped of a pot, whereby a bottom 33 points in the direction of the first media chamber 9. Two grooves 35, in which guide rings 37 are arranged, are arranged at a certain distance from each other along the peripheral side of the limiting piston 5. A further circumferential groove 39, in which a sealing element 41 is arranged, is provided between the guide rings 37. The separating member 5 is formed to increase the storage reservoir of gaseous and insofar compressible fluid in the manner of a pot or trough and has a collecting device 43 on the bottom side for the incompressible fluid, which may inadvertently arrive at the gaseous side from the oil side of the accumulator via the sealing device having a sealing element 41. The collecting device 43 is shaped insofar in the form of a reservoir coaxial to the longitudinal axis LA in the limiting piston 5. This collecting device 43 is thus arranged adjacent opposite or facing the ultrasonic sensor 13 in its direct sound-emitting direction.

(7) A sleeve-shaped sensor holder 45 is inserted, in particular screwed, in the lid part 19 adjacent to the second media chamber 11. The sensor holder 45 has adjacent to the outer side 47 of the lid part 19 a threaded segment 49 and an enlarged head 51. An annular sealing element 53 is provided between the head 51 and the lid part 19. On the inside 55 the sensor holder 45 is hollow to form a sensor chamber 57. The inside 55 of the sensor chamber 57 is connected by a media channel 59 in a media-carrying manner or in fluid communication to the second media chamber 11 having the compressible fluid in the form of the working gas. For this purpose, the sensor chamber 57 has multiple passage points 59 in the form of bores between a structure 61 of the ultrasonic sensor 13 and the bottom side 63 of lid element 19 facing the separating element.

(8) In the lid part 19 adjacent to or at one end of the second media chamber 11, the ultrasonic sensor 13 is held in the sensor holder 45. The ultrasonic sensor 13 performs its position detection of the separating element 5 on the side of the second media chamber 11 having the compressible fluid. The ultrasonic sensor 13 is arranged coaxially to the longitudinal axis LA of the housing 7. Its end is held in the sensor chamber 57. The ultrasonic sensor 13 is arranged stationary on the lid part 19 in such a manner that at least part of the sensor chamber 57 having the media router 59 protrudes by a predetermined projection U into the second media chamber 11 having the compressible fluid. In every traversing position of the separating element 5, sensor 13 is kept at a distance from the separating element 5. As a result, the ultrasonic sensor 13 is held pressure-compensated in the second media chamber 11. In particular, the sensor 13 can also be held in the top dead center of the piston-shaped separating element 5 in the pot-shaped recess of the separating element 5 having the collecting device 43, without risk of being struck, and in doing so conduct sensor measurements.

(9) The ultrasonic sensor 13, which is shown in more detail in FIG. 2, has an ultrasonic transducer 65 with a disc-shaped piezoceramic 66 disposed on the likewise disc-shaped structure 61 by full-surface bonding. The structure 61 seals the sensor chamber 57 from the second media chamber 11 having the compressible fluid. To this end, the support 61 has a circumferential groove 67. Support 61 is securely held via an o-ring 69 located in an inner circumferential groove 71 of the sensor chamber 57. Due to electrical excitation, the piezoceramic 66 can expand or contract radially and transfer this change in length to the structure 61, resulting in a periodic deflection of the structure 61, which in particular bulges and that way produces the desired sound wave.

(10) The second media chamber 11 contains a reference measuring section inside the sensor chamber. The reference measuring section is delimited by two reference points 13, 73, arranged stationary in relation to each other. One or first reference point is the ultrasonic sensor 13 itself. The other or second reference point is a reflection point 73 for the sensor signal. This second reflection point 73 is formed by a boundary wall, here a step in the inner wall of the sensor chamber 57. The reflection point 73 and the separating element 5 are thus arranged advantageously on opposite sides of the ultrasonic sensor 13. The measuring section and the reference section are therefore independent of each other. In addition, the reflection point 73 is provided at a protected location, preventing any influence on part of the separating element 5.

(11) The sensor chamber 57 is covered in the direction of the environment by a glass part 79, preferably in the form of a glass feedthrough. The ultrasonic sensor 13 is connected to a control unit 85 through the glass part 79 via a cable connection 83.

(12) The ultrasonic sensor 13 is operated at a pre-determinable operating frequency. This frequency can be selected between a low frequency and a comparatively higher frequency. The lower frequency is chosen so that a small wave-dependent amplitude modulation, and therefore little dispersion, occurs, and is particularly 100 kHz. At the higher frequency, a higher resolution is possible for the displacement measurement due to the shorter wavelength. The higher frequency is preferably 150 kHz.

(13) The functionality of the ultrasonic displacement measuring system 1 according to the invention is explained below. The ultrasonic displacement measuring system 1 is arranged in a hydropneumatic pressure accumulator 3. Due to the storage of an incompressible or compressible medium in the first media chamber 9, the separating element 5 is moved inside the pressure accumulator 3, to provide pressure compensation between the fluids in the two media chambers 9, 11. Meanwhile, the position of the separating element 5 can be determined using the ultrasonic displacement measuring system 1. For this purpose, a sound signal, controlled by the control unit 85, is emitted by the ultrasonic sensor 13. The reverberations at the separating element 5 and at the ultrasound sensor 13 opposite reference point 73 are detected, resulting in the propagation delays of reflected sound waves being determinable using the control unit 85. The sound propagation velocity in compressible fluid of the second media chamber 11 is determined from the propagation delay of the sound signal from the ultrasonic sensor 13 to the assignable reference point 73 and back. From this sound propagation velocity and the propagation delay of the sound signal from the ultrasonic sensor 13 to the separating element 5 and back, the respective distance A of the movable separating element 5 from the stationary ultrasonic sensor 13 can then be determined.

(14) If liquid was to penetrate from the first media chamber 9 having the incompressible fluid through a gap 87 between the separating element 5 and housing 7 into the second media chamber 11, it would flow into the collection device 43. There, it shortens the measuring section between the ultrasonic sensor 13 and the separating element 5. As, however, part of the ultrasonic wave continues to be reflected at the bottom of the separating element, the ultrasonic displacement measuring system 1 according to the invention can be advantageously used to determine whether and how much liquid has penetrated into the second media chamber. This determination includes the no longer sufficient tightness of the sealing system 41 of the separating piston 5 and triggers in this respect a regular maintenance of the accumulator or even its exchange in the connected hydraulic circuit (not shown).

(15) The invention thus presents a particularly advantageous ultrasonic displacement measuring system 1. By measuring at the gas side 11, the position of the separating element 5 can be detected very precisely, because the ultrasonic signal has to propagate only through a fluid. Regardless of the movement of the separating element 5 and the ambient conditions, no phase transitions occur in this compressible fluid, i.e. related measurement errors need not be considered. Due to the fact that the compressible fluid usually is a gas, the electrically controlled ultrasonic sensor 13 is always stored in a dry environment, i.e. during operation no impairment of the ultrasonic sensor 13 by moisture needs to be feared. The ultrasonic measurement system 1 is therefore durable and low maintenance. The components required for the ultrasonic sensor 13 are also available at relatively low cost. The minimum displacement measuring section for the sensor 13 is formed by the bottom dead-center position of the piston-shaped separating element 5, as soon as this comes into contact with the upper surface of the lower lid part 19 facing the separating elements 5.

(16) The solution according to the invention can on its merits also be used for pneumatic power cylinders (not shown), in which the two media chambers 9, 11 are separated from each other by a piston-rod unit. The rod of the respective unit is guided to the outside at one lid side for linking to third components. The two media chambers 9, 11 can be alternately connected to a pneumatic supply to reciprocate the piston-rod unit.

(17) While one embodiment has been chosen to illustrate the invention, it will be understood by those skilled in the art that various changes and modifications can be made therein without departing from the scope of the invention as defined in the claims.