The invention relates to a measuring sensor under pre-stress for measuring forces and/or moments.
Measuring sensors are inter alia used as stackable machine elements for the installation into machine or device elements transmitting force and/or moments to measure forces, pressures, accelerations, expansions and moments. Such measuring sensors may be piezoelectric, piezoresistive, optical, capacitive or based on strain gages (DMS). In the following, piezoelectric measuring sensors will be mainly detailed. In these for example, suitable crystals having piezoelectric characteristics in the form of thin discs are incorporated into a sleeve in a centered manner and welded under a membrane exerting a desired pre-stress to the crystals. On the one hand, the pre-stress ensures that the measurement is effected in the linear measuring range of the sensor. On the other hand, also a signal within the linear measuring range of the sensor is generated thereby if negative forces (tensile forces) or vibrations are measured.
However, the level of the measurable tensile forces is too low for many applications with large tensile forces and is limited by the tensile stability of the welding of the membrane to the sleeve of the sensor. To be able to measure higher tensile forces or shearing forces the sensor is incorporated between two adaptor elements by means of a centering sleeve in a centered manner and is placed under an additional pre-stress by means of a suitable screw connection of the adaptor elements.
The arrangement described herein as prior art exhibits certain disadvantages. On the one hand, the overall height of such measuring arrangements is often very large. On the other hand, two centerings (of the crystals in the sensor and of the sensor in one of the adaptor elements) have to be conducted, which is quite elaborate.
The object of the present invention is to provide a sensor and a measuring arrangement for both positive and negative forces, pressures, accelerations, expansions, shearings and/or moments, which require a small overall height and which enable a simple and cost effective manufacture in the configuration thereof.
According to the present invention, this object is solved by the characterizing part of claim 1.
In the following, the invention is detailed with respect to the Figures, in which:
a illustrates a further example of an embodiment of the invention of a measuring sensor under pre-stress with an integrated amplifier module, in a cross-sectional view;
b illustrates the same example of
One membrane 14 covers these crystal plates. It is attached under pre-stress by means of welding joints 15 to sleeve 13. At sleeve 13, there also is a suitable connection plug 18 at which the signal generated by the crystals 12 may be transmitted and analyzed. Between two adaptor elements 16a and 16b, the sensor 11 is incorporated by means of a centering sleeve 17 in a centered manner and is placed under additional pre-stress by means of a suitable connection device 19 connected to the adaptor elements 16. These adaptor elements 16 exhibit suitable attachment devices 20 for the components or elements which are placed under pressure and tension and which are to be measured (not shown in the drawings). Additionally, the adaptor elements 16 may include suitable engaging devices 24 for tools, e.g. by a partially flat or hexagonal embodiment of the edge, enabling a force impact by means of a tool, e.g. a hexagonal wrench.
The adaptor sleeve 22 is formed in a solid manner and combines according to the present invention all functions of sleeve 13, of the adaptor element 16a and the centering sleeve 17 in one single element. By the combination of the three parts (13, 16a, 17) the centering of the sensor 11 in an adaptor element is omitted. By means of the connection device 19 which preferably is formed as a screw thread the adaptor element 16 is attached to the adaptor sleeve 22 whereby sensor 11 is placed under pre-stress.
The adaptor sleeve 22 has a connection plug 18 for the signal transmission as well as an attachment device 20 for mounting to a component placed under pressure and tension (not shown in the drawings) and has an engaging device 24 as a working surface for tools as described under
The attachment device 20 described herein may consist of one or more, preferably three attachment sites, which are e.g. formed as a screw bore and arranged on the adaptor sleeve in a spaced manner. By the use of several attachment sites, the dimensions thereof may be decreased, since the force of the components placed under pressure and tension is distributed to the number of attachment sites. Further, the center of the arrangement 21 of the present invention remains free for a mounting through bore 23, which may also be used for attachment at the components under pressure and tension. For this purpose, a protrusion at the adaptor element 16 or at the adaptor sleeve 22 in the region of the mounting bore 23 may serve to e.g. hold a screw. This screw may be attached to a suitable tool through the mounting bore.
By the arrangement 21 of the present invention of the attachment device 20 the height of the now single adaptor element 16 may be substantially lower than the adaptor element 16b of
A further advantage of said embodiment is that the adaptor element 16 may easily be replaced by another one which exhibits an attachment device 20 adapted to a special application.
a illustrates an embodiment of the present invention of a measuring sensor with integrated amplifier arrangement.
b shows the same arrangement cut in A-A with the same designations.
In this arrangement the connection device 19 of the adaptor element 16 with the adaptor sleeve 22 is attached in adaptor sleeve 22, whereas said connection device 19 in the arrangement of
In
Additionally, in
According to the invention, the adaptor sleeve 22 of
In particular, such measuring sensors may be piezoelectric, piezoresistive, optic, capacitive or on the basis of strain gages (DMS).
A further embodiment of the present invention of a measuring sensor 29 with external amplifier arrangement is illustrated in
Alternatively, the adaptor sleeve 22 may posses an integrated amplifier casing 31, in which the amplifier arrangement 27 may be introduced. By the integration of adaptor sleeve 22 with the amplifier arrangement 27 the connection area 31 can be omitted.
This embodiment also represents a measuring sensor which has a much lower overall height than a measuring sensor built according to the prior art.
Each of the inventive measuring sensors 21, 25, 29 disclosed herein is characterized by its compact design and the thus small height as well as the possibility for simple and cost effective manufacture, since less elements are used and only one single centering has to be carried out. Also, the amplifier modules may be integrated into the arrangement in very different manners. The person skilled in the art can easily conceive further embodiments, arrangements and extensions, e.g. an integration of memory chips for calibration values. In particular, all combinations of the features of the individual embodiments described may easily be prepared without difficulties.
List of Designations
10. measuring sensor as prior art
11. sensor
12. crystal discs (piezo crystal)
13. sleeve
14. membrane
15. welding joint
16. adaptor elements
17. centering sleeve
18. connection plug
19. connection device of the adaptor elements
20 attachment device to components, elements
21. embodiment of the present invention of a measuring sensor
22. adaptor sleeve
23. mounting bore
24. device as a working surface for tools
25. embodiment of the present invention of a measuring sensor with internal amplifier arrangement
26. recess
27. amplifier arrangement
28. electronic components
29. embodiment of the present invention of a measuring sensor with external amplifier arrangement
30. connection area
31. amplifier casing
32. nut
Number | Date | Country | Kind |
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017403 | Feb 2003 | CH | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/CH04/00064 | 2/5/2004 | WO | 7/13/2006 |