Position sensor detecting a mechanical pulse conducted by a waveguide formed of magnetostrictive material

Abstract

A position sensor comprises a waveguide of magnetostrictive material which extends along a measurement path and which is configured for conducting mechanical pulses triggered by magnetostriction. A transducer at a first end of the waveguide serves for coupling a current pulse into the waveguide and for detecting a mechanical pulse conducted by the waveguide in the direction of the transducer. A damping element of an elastomer material is provided at a second end of the waveguide for damping a mechanical pulse propagating in the direction of the second end, wherein the hardness of the elastomer material increases as the distance from the transducer increases. The invention furthermore relates to a method of manufacturing a damping element of such a position sensor.

Claims

1. A position sensor comprising a waveguide of magnetostrictive material which extends along a measurement path and which is configured for conducting mechanical pulses triggered by magnetostriction; a transducer arranged at a first end of the waveguide, the transducer being configured to couple a current pulse into the waveguide and to detect a mechanical pulse conducted by the waveguide in the direction of the transducer; and a damping element of an elastomer material arranged at a second end of the waveguide, the damping element being configured to damp a mechanical pulse propagating in the direction of the second end, wherein the hardness of the elastomer material increases as the distance from the transducer increases, wherein the elastomer material is formed directly at the waveguide with the aid of a casting process; and wherein the elastomer material is a material comprising at least two components whose mixing ratio determines the hardness of the elastomer material.

2. The position sensor in accordance with claim 1, wherein the hardness of the elastomer material in the damping element continuously increases as the distance from the transducer increases.

3. The position sensor in accordance with claim 1, wherein the mixing ratio of the components in the damping element changes continuously with the distance from the transducer.

4. The position sensor in accordance with claim 1, wherein the elastomer material is formed onto the waveguide with the aid of an injection molding process.

5. The position sensor in accordance with claim 1, wherein the waveguide has a non-linear extent within the damping element to extend the damping path.

6. A method of manufacturing a damping element of a position sensor, the position sensor comprising a waveguide of magnetostrictive material which extends along a measurement path and which is configured for conducting mechanical pulses triggered by magnetostriction; a transducer arranged at a first end of the waveguide, the transducer being configured to couple a current pulse into the waveguide and to detect a mechanical pulse conducted by the waveguide in the direction of the transducer; and the damping element, wherein the damping element is formed of an elastomer material and is configured to damp a mechanical pulse propagating in the direction of the second end, wherein the hardness of the elastomer material increases as the distance from the transducer increases, and, the method comprising the steps of: casting the elastomer material around the second end of the waveguide in a casting process and wherein the casting process comprises the casting of a casting material comprising at least two different components whose mixing ratio is set along the damping element to be cast in dependence on the spacing from the transducer.

7. The method in accordance with claim 6, wherein the elastomer material is injection molded around the second end of the waveguide.

8. The method in accordance with claim 7, wherein the mixing ratio is changed continuously in dependence on the spacing from the transducer.

9. The method in accordance with claim 7, wherein the casting material comprises an at least two-component silicone material.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be described in the following by way of example with reference to the drawings.

(2) FIG. 1 is an exploded representation of a position sensor in accordance with the invention;

(3) FIG. 2 is an explanatory cross-sectional representation of a waveguide in an installed state;

(4) FIG. 3 is a schematic representation of a damping element of a first embodiment of the position sensor;

(5) FIG. 4 is a schematic representation of a damping element of a second embodiment of the position sensor;

(6) FIG. 5 is a schematic representation of a damping element of a third embodiment of the position sensor;

(7) FIG. 6 is a schematic representation of a damping element of a fourth embodiment of the position sensor;

(8) FIG. 7 is a schematic representation of a damping element of a fifth embodiment of the position sensor; and

(9) FIG. 8 is a schematic representation of a damping element of a sixth embodiment of the position sensor.

DETAILED DESCRIPTION

(10) The position sensor 11 shown in an exploded representation in FIG. 1 comprises a waveguide housing 13 in the form of an elongated pipe of stainless steel to whose one pipe end a sensor head housing 15 is attached. The other pipe end is closed by an end cap 17. A waveguide 19 of a magnetostrictive material is located in the waveguide housing 13. The waveguide 19 is preferably a wire of ferromagnetic material and, starting from a control unit 21, extends axially, that is in parallel with the longitudinal axis L of the waveguide housing 13 and through said waveguide housing up to a damping element 23 which is held in the waveguide housing 13 using a sleeve 24. The sleeve 24 can, for example, be the injection mold in which the damping element 23 is cast in a shape still to be described. In the region of the damping element 23, the waveguide 19 merges over a bent region 28 into a return conductor 25 which again leads back to the control unit 21. The waveguide 19 is held in the waveguide housing 13 by means of a positioning element 27 and an intermediate pipe 29. The waveguide 19 is configured as having the shape of a wave in the region of the damping element 23 in order to extend the damping path.

(11) A transducer 30 is associated with the control unit 21 and comprises a bar magnet 31, which is fixedly soldered to the waveguide 19, and a coil 32 surrounding said bar magnet. The transducer 30 can convert torsion pulses conducted by the waveguide 19 into electrical position signals, such as is generally known, for example from EP 0 882 212 B1. A transducer receiver 33 is associated with the transducer 30 and, like the control unit 21, is attached to a circuit board 35. In FIG. 1, the following individual parts of the control unit 21 are, for reasons of clarity, shown separately again laterally next to the control unit 21: the transducer 30, bar magnet 31, coil 32 and transducer receiver 33.

(12) The circuit board 35 with the components mounted thereat is accommodated in the sensor head housing 15. Said sensor head housing is closed by a cover part 37 which is provided with latching teeth 41 at its boundary 40. The latching teeth 41 are configured for engaging behind an inwardly projecting bead 43 of the sensor head housing 15. The cover part 37 can thus be plugged onto the sensor head housing 15 and can be permanently latched thereto on the plugging on. The sensor head housing 15 can be installed into a hydraulic cylinder using a sealing ring 42 and a support ring 44, such as is disclosed in DE 20 2006 012 815 U1, for example.

(13) Contact pins 45 are provided at the cover part 37 for the connection of the position sensor 11 to a power supply and to a reception unit (both not shown). The contact pins are angled as shown in order to enable the connection of a connection plug or of a connection socket from the side. The position to be detected by the position sensor 11 is marked by a position magnet 47 which is of ring shape here and surrounds the waveguide housing 13. The position magnet 47 is fastened to a component which is not shown and whose position should be detected, e.g. to a displaceable piston of a hydraulic cylinder.

(14) FIG. 2 shows the waveguide 19 and the positioning element 27 in a cross-sectional view in an installed state. The positioning element 27 is produced from an elastic and non-magnetic material, e.g. from silicone, and can therefore be deformed. If it is in the undeformed starting state not shown here, it has a trapazoidial-like outer cross-sectional shape. A recess 50 having a cross-sectional shape in the form of a keyhole extends through the entire positioning element 27 in the axial direction. The waveguide 19 is then arranged in the wide reception section 51 of the recess 50. In the installed state, which is shown in cross-section in FIG. 2, the positioning element 27 is pressed together and jams in the intermediate pipe 29 which is e.g. produced from polytetrafluoroethylene by causing the intermediate pipe 29 to expand by opening at gap 55. The unit formed by the waveguide 19, the positioning element 27 and the intermediate pipe 29 is positioned in the waveguide housing 13 in the installed state. The intermediate pipe 29 contacts the inner wall 57 of the housing 13 over its full area, with the exception of gap 55, in the example shown. Due to the trapazoidial-like outer cross-section of the positioning element 27 in the undeformed state, said positioning element does not contact the intermediate pipe 29 over its full area, but rather only at the corner regions 59. Free spaces 60 are formed between said corner regions and can be used for the leading through of electrical lines and of the return conductor 25 (FIG. 1). Due to the positioning element 27 and to the intermediate pipe 29, the waveguide 19 in this example is held centered in the waveguide housing 13, on the one hand, and is protected from excessive deflections, shocks and vibrations, on the other hand.

(15) FIGS. 3 to 8 show damping elements of different embodiments of the positioning sensor.

(16) This region of the position sensor is shown at the top right in FIG. 1; the damping element 23 and the sleeve 24 surrounding it can be recognized in said region in the exploded representation of FIG. 1. An embodiment is shown in FIG. 1 as it is represented in FIG. 3.

(17) FIG. 3 shows this region of the position sensor 11 in a schematic representation in greater detail. The waveguide 19 can be recognized which is configured as wave-shaped in the region 26. It is surrounded by a casting mold 24. Two-component silicone can e.g. be injected through the injection passage 70 into this casting mold and surrounds the wave-shaped waveguide 19 in the hollow space shown after the injection molding process and the hardening process. In this manner, the injected material becomes a damping element 23 after a correspondingly selected hardening process. Depending on the embodiment, the casting mold 24 can remain at the waveguide or it can be removed. The mixing ratio of the two silicone components of the injected material continuously changes during the injection process through the injection passage 70. The hardness of the hardened material changes in this manner when the components are selected such that one of the components has a greater hardness than the other one after the hardening. The two components of the silicone can thus e.g. be selected such that with a ratio of 1:1 a hardness of less than a Shore hardness of 0 is present, whereas a Shore hardness of 30 is present with a mixing ratio of 2:1. The hardness of the damping element 23 is in this respect set such that it increases in the arrow direction 72 shown. If the hardness increases in the arrow direction, a mechanical pulse, which propagates from the left along the waveguide 19 in FIG. 3, is first incident at a very soft elastomer material in order to minimize the reflection, wherein the material becomes harder along the path to the right due to the greater density and results in a greater damping.

(18) FIG. 4 shows a damping element 23 of another embodiment in which the casting mold 24 has a conical extent in the left region of the damping element 23 in order to provide a further adaptation possibility with respect to the damping requirements. In a manner not shown, other shapes can also be selected to optimize an adaptation to the conditions.

(19) FIG. 5 shows a design in which the waveguide does not have the shape of a wave in the region of the damping element, but rather extends in a linear manner through the damping element.

(20) FIG. 6 shows an embodiment which corresponds to the design of FIG. 4 with a linear waveguide.

(21) FIG. 7 shows a further embodiment in which the damping element 23 comprises individual elements 23, 23 and 23. They are generated in a specific mold 24 in which the two-component silicone is introduced through three injection passages 70 to produce the damping element 23. In this respect, a different mixing ratio for the two components of the silicone is selected for the different regions 23, 23, 23. A step-wise increase in the hardness of the damping element 23 can be achieved in this manner.

(22) With the invention, a damping element is possible which combines the advantages of a simple casting process in the manufacture with the advantages of a damping element having a hardness increasing in the axial direction.

(23) The present description frequently mentions silicone, in particular e.g. multicomponent silicone. Other materials having corresponding properties can likewise be used, for example polyurethane.

LIST OF REFERENCE NUMERALS

(24) 11 position sensor

(25) 13 waveguide housing

(26) 15 sensor head housing

(27) 17 end cap

(28) 19 waveguide

(29) 21 control unit

(30) 23 damping element

(31) 23, 23, 23 individual element

(32) 24 sleeve

(33) 25 return conductor

(34) 27 positioning element

(35) 28 bent-over region

(36) 29 intermediate pipe

(37) 29 arrangement

(38) 30 transducer

(39) 31 bar magnet

(40) 32 coil

(41) 33 transducer receiver

(42) 35 circuit board

(43) 37 cover part

(44) 40 boundary

(45) 41 latching tooth

(46) 42 sealing ring

(47) 43 bead

(48) 44 support ring

(49) 45 contact pin

(50) 47 position magnet

(51) 50 recess

(52) 51 reception section

(53) 57 inner wall

(54) 59 corner region

(55) 60 free space

(56) 70 injection passage

(57) 72 increase in hardness

(58) L longitudinal axis