System for position measuring and integrity measuring

Abstract

A system for measuring the position of a rod element as, for example, a hydraulically or pneumatically operated piston rod. Unlike the prior art, the system according to the present invention employs a measuring principle that does not require preparatory treatment of the rod element as is required in the known solutions. The system employs direct time of flight measurements with the aid of acoustic surface waves that are introduced into the rod element. The instrument is retrofittable on existing cylinders without any modification/reconstruction thereof. An EMAT principle is employed to introduce the surface waves into the measurement in a non-contact manner.

Claims

1. A system for a pneumatic or hydraulic cylinder, linear guide, damper, or rod element, adapted to provide position measurement by the distance to one and/or both ends of a translatory and/or rotary element, wherein an ultrasound-based time of flight measurement is used directly in the translatory and/or rotary element, and that sound waves for the time of flight measurement are generated by a sensor in the form of an EMAT which generates and detects the sound wave, wherein permanent magnets of the sensor are distributed around a circumference of the translatory and/or rotary element and the permanent magnets have a corresponding orientation in the radial direction of the translatory and/or rotary element with respect to their individual north and south orientation.

2. A system according to claim 1, wherein permanent magnets of the sensor are arranged in a torus with an extent covering the whole or parts of a circle surrounding the translatory and/or rotary element in which the sound wave is desired to be introduced and detected.

3. A system according to claim 2, wherein the sensor is mounted onto the pneumatic or hydraulic cylinder, linear guide, damper or rod element without any preparatory treatment of the cylinder body and/or rod elements.

4. A system according to claim 2, wherein the sensor is integrated in a cylinder housing termination.

5. A system according to claim 1, wherein permanent magnets of the sensor are arranged in a torus and have an arc-shaped cross-section with an extent covering the whole or parts of a circle surrounding the translatory and/or rotary element in which the sound wave is desired to be introduced and detected.

6. A system according to claim 5, wherein the sensor is mounted onto the pneumatic or hydraulic cylinder, linear guide, damper or rod element without any preparatory treatment of the cylinder body and/or rod elements.

7. A system according to claim 5, wherein the sensor is integrated in a cylinder housing termination.

8. A system according to claim 1, wherein the sensor is mounted onto the pneumatic or hydraulic cylinder, linear guide, damper or rod element without any preparatory treatment of the pneumatic or hydraulic cylinder, linear guide, damper, or rod element.

9. A system according to claim 8, wherein the sensor is integrated in a cylinder housing termination.

10. A system according to claim 1, wherein the sensor is integrated in a cylinder housing termination.

11. A system for a pneumatic or hydraulic cylinder, linear guide, damper, rod elements, or axles, adapted to provide integrity measurements of a translatory and/or rotary element with the aid of reflections from acoustic impedance changes due to cracks and damage, wherein waves for the integrity monitoring are generated by a sensor in the form of an EMAT which generates and detects a sound wave and is fixedly installed, but where the monitored object is able to rotate and/or translate relative to the sensor, wherein permanent magnets of the sensor are distributed around a circumference of the translatory and/or rotary element have a corresponding orientation in the radial direction of the translatory and/or rotary element with respect to their individual north and south orientation.

Description

EXAMPLE

(1) In order to give a better understanding of the different technical features and the functions of the present invention a non-limiting exemplary description of an embodiment is given below. The description is given with reference to the drawings, wherein

(2) FIG. 1 shows a typical cylinder with which a system according to the present invention can be used;

(3) FIG. 2 is a schematic basic diagram of a sensor in the system according to the present invention and a part of a typical cylinder rod;

(4) FIG. 3 is a schematic basic diagram of an embodiment of an aspect of radial permanent magnets in the system according to the present invention;

(5) FIG. 4 shows a meander-shaped coil in the system according to the present invention before bending as part of its installation in the sensor;

(6) FIG. 5 is a system diagram for a measuring device in the system according to the present invention;

(7) FIG. 6 shows another embodiment of the measuring device shown in FIG. 5;

(8) FIG. 7 shows an embodiment of the sensor in the system mounted on a hydraulic cylinder;

(9) FIG. 8 shows a piezoelectric solution with contact slide;

(10) FIG. 9 shows a piezoelectric solution with spherical contact element; and

(11) FIG. 10 shows the principle of integrity monitoring by means of the sensor.

(12) In FIG. 1 can be seen a typical cylinder 1 in cross-section, the figure indicating a distance (I) between a cylinder seal 5 and an eye 4 mounted at the end of a rod element 3. A distance (I′) is also marked and indicates the distance from the seal 5 to the piston element 2 of the cylinder 1. A dividable sensor 6 is mounted around the cylinder rod 3 with the object of providing time of flight measurements in said rod element 3. The sound waves are generated in the sensor 6 and conducted into the rod element 3, where they propagate in the longitudinal direction of the rod element 3. The sound waves spread in both directions, such that they meet the termination of the rod element 3. At one end, the sound waves meet the termination of the rod element 3 where, for example, an eye 4 is mounted. At the other end, the sound waves meet a termination in the form of a transition to a piston element 2. In solutions where a plunger is used, the rod element 3 is terminated without a piston element 2.

(13) The distance to the rod element 3 is calculated in that the speed of sound in the material of the rod element 3 is known. An acoustic surface wave with planar wave front is induced in the surface of the acoustic medium, which acoustic medium in this case is the rod element 3, and the time is measured from the transmission of the acoustic surface wave until the reflection of the pulse from the end/ends of the rod element 3 is received back by the sensor 6. The speed of sound in the material of the rod element 3 is known, such that the distance that the sound has covered can be calculated. The speed of sound of Rayleigh surface waves in different materials can be determined by calibration, i.e., placing TX and RX at a known distance s.sub.k and measuring the transit time τ.sub.k. The speed of sound in the medium can then be determined from the formula c=s.sub.k/τ.sub.k. When subsequent measurements are made with random distance, it will be possible to determine the distance from the formula s=c.Math.τ.

(14) FIG. 2 shows a schematic basic diagram of the sensor 6 and a part of a typical cylinder rod 3. The sensor 6 comprises a plurality of radially oriented permanent magnets 7 that are mounted in a holder (not shown), the permanent magnets 7 being distributed around the whole or parts of the circumference of the rod element 3. The permanent magnets 7 are so arranged that they have coinciding north/south orientation and surround an antenna 9 in the form of a meander coil 14. Electric current (indicated by vector arrows in and out of the sheet of paper) in the meander coil 14 generates, in interaction with the field from the permanent magnets 7, eddy current 10 (indicated by vector arrows in and out of the paper) with resulting Lorentz forces 11 (indicated by vector arrows in and out of the paper) in the rod element 3, these forces generating an acoustic surface wave that is used in the measurement.

(15) The permanent magnets may, for example, be configured with a toroidal shape and/or an arc-shaped cross-section.

(16) FIG. 3 is a basic diagram showing how the permanent magnets 7 are arranged around the rod element 3. The meander coil 14 is also shown and the whole arrangement is encased in a housing 15 that can be opened in order to encircle the rod element 3.

(17) FIG. 4 shows the meander coil 14 in greater detail, the meander coil 14 being shown in unrolled state, where the meander coil 14 when arranged in the housing 15, will surround the rod element 3 and be arranged within the radial permanent magnets 7.

(18) FIG. 5 is a schematic illustration of a measuring device in the system according to the present invention, where a unit 100 comprises a power supply, an arithmetic unit and an operator interface, unit 102 comprises a signal transmitter with associated electronics, unit 103 comprises a signal receiver with associated electronics. The measuring device further comprises an EMAT TX unit 111 and an EMAT RX unit 112. By connecting the different units as shown, a distance 106 in, for example, the rod element 3 can be determined.

(19) The measuring device in the system measures the distance between TX and RX by measuring the time acoustic Rayleigh surface waves take to travel from the TX unit 111 to the RX unit 112. The speed of sound of Rayleigh surface waves in different materials can be determined by calibration, i.e., by placing TX unit 111 and RX unit 112 at a known distance s.sub.k (not shown) and measuring the transit time τ.sub.k. The speed of sound in the medium can then be determined from the formula c=s.sub.k/τ.sub.k. When subsequent measurements are made with random distance s.sub.k, it will be possible to determine the distance from the formula s=c*τ.

(20) If the transmitted signal is sufficiently powerful, a receiver in the unit 103 will also receive signals reflected from the two ends of the rod element 3, this allowing position determination of the rod element's 3 ends relative to the transmitter and receiver position.

(21) FIG. 6 is a schematic illustration of another embodiment of a measuring device in the system according to the present invention, where a unit 100 comprises a power supply, an arithmetic unit and an operator interface, a unit 102 comprises a signal transmitter with associated electronics, and a unit 103 comprises a signal receiver with associated electronics. The measuring device further comprises an EMAT TX/RX unit 109 and a reflector 108. By connecting the different units as shown, a distance 106 in, for example, the rod element 3 can be determined. This measuring system is based on the same principles as the measuring device according to FIG. 5, but here the RX and TX antenna will be assembled in one unit 109. In this solution a TX/RX switch 110 is used.

(22) A reflector 108 is introduced in the form of a groove milled in the surface perpendicular to the longitudinal direction of the rod element 3, around the circumference of the rod element 3. Alternatively, a collar (not shown) with a sharp edge can be arranged around the rod element 3, after which the collar is pressed into the surface of the rod element 3. The object is to create a discontinuity in the acoustic impedance that the surface waves meet in order to reflect the wave. The reflector 108 is thus a fixed part of the rod element 3 and will therefore follow the movements thereof.

(23) The distance is now given by the formula s=c.Math.τ.

(24) If the system is regarded as though an EMAT TX/RX is attached to the end of a cylinder from which the piston rod 3 exits, and given that the rod element 3 in FIG. 6 is a piston rod, we will have a system that can determine the position of the piston element 2 (or also the “eye” 4 end of the piston rod 3).

(25) FIG. 7 shows a possible embodiment of the system according to the present invention mounted on a typical hydraulic cylinder.

(26) FIG. 8 shows a sensor arrangement with a slider 116 shaped in conformity with the rod element 3, where a piezoelectric transducer 117 lies pressed against 116 by the spiral spring 118. The spiral spring gives the necessary contact pressure between the part in the arrangement and the rod element 3. The sensor is mounted in a housing (not shown).

(27) FIG. 9 shows a sensor arrangement where a ball 120 is non-rotationally mounted in a holder 121. A piezoelectric transducer 122 is pressed against the upper edge of the holder 121 by a spiral spring 123. The spiral spring presses the arrangement against the rod element 3. The sensor is mounted in a housing (not shown).

(28) FIG. 10 is a schematic illustration of a measuring device for integrity monitoring. The sound waves 131 from the sensor 6 are reflected in the crack 130 as a result of the change in acoustic impedance, which is then registered by the sensor.

(29) The system according to the present invention is, however, not limited to being used in connection with different pneumatic or hydraulic cylinders, but can also be used on different rod elements or the like where position measurement is desirable.

(30) It should be noted that several embodiments are possible. The scope of the invention is limited by the claims, and a person of skill in the art will be able to make numerous changes to the aforementioned examples without departing from the scope of the invention.