Surveillance system

• US 5,412,582 A
• Filed: 06/29/1992
• Issued: 05/02/1995
• Est. Priority Date: 07/08/1991
• Status: Expired due to Fees

• Current Assignee: Scan-Mag Sense As
• Original Assignee: Scan-Sense A/S
• Inventors: Althoff, Fredrik, Larsson, Thomas, Hesthamar, Tore
• Primary Examiner(s): Ramirez, Ellis B.
• Application Number:
  US07/905,366
• Time in Patent Office: 1,037 Days
• Field of Search: 364/507, 364/508, 73/862.333, 73/862.474
• US Class Current: 702/43
• CPC Class Codes: F16B 31/028 with a load-indicating washer or washer assembly
• CPC Class Codes: G01L 5/243 using washers

Abstract

The present invention relates to a surveillance system for measuring and surveying e.g. the preload in screws (23) or similar. It comprises a number of sensor systems (1) electrically connected to a common electronic and computing system, each said sensor system (1) comprising sensor means (2) being provided with a magnetoelastic material (6) sensitive to the preloads and a sensing device (3) comprising a coil system at least partly surrounding the sensitive material (6). The sensitive material (6) is excited via the coil system with a frequency of at least 300 kHz so as to make the system insensitive to external disturbing fields.

Claims

1. Surveillance system for measuring and surveying the preload in screws, bolts or similar objects, comprising:

at least one sensor system having sensor means arranged on the screws, bolts or similar objects, said sensor means including a magnetoelastic material sensitive to loads to which the screws, bolts or similar objects are exposed;

a sensing device having a coil system for exciting said magnetoelastic material;

each said sensor means further being partly or completely surrounded or covered by said coil system;

each said coil system further being electrically connected to an electronic system for monitoring loads sensed by said sensor and to a common computing system;

wherein the magnetoelastic material is excited with a frequency of at least 300 kHz.

2. Surveillance system according to claim 1, wherein the magnetoelastic material is excited with a frequency of between 500 kHz and 10 MHz.

3. Surveillance system according to claim 1, wherein the magnetoelastic material is excited with a frequency of 1-2 MHz.

4. Surveillance system according to claim 1, wherein the magnetoelastic material comprises a magnetoelastic amorphous material.

5. Surveillance system according to claim 1, wherein the magnetoelastic material is applied essentially axially on the sensor means.

6. Surveillance system according to claim 1, wherein the magnetoelastic material comprises magnetoelastic ribbons, said ribbons being attached to the sensor means and forming a ribbon belt.

7. Surveillance system according to claim 1, wherein the sensor means comprises a washer either separate, securely attached to, or in one piece with a screw, bolt, nut or similar.

8. Surveillance system according to claim 1, wherein the coil system partly or completely, essentially axially, encloses the sensor means.

9. Surveillance system according to claim 1, wherein the coil system comprises coils carrying out both an excitation-, and a pick-up-function either separately or in one combined coil.

10. Surveillance system according to claim 1, wherein a magnetoelastic material is chosen such that the temperature coefficient of the material essentially corresponds to that of the object to be measured.

11. Surveillance system according to claim 10, wherein the magnetoelastic material is a Ni-based amorphous material.

12. Surveillance system according to claim 1, wherein electronic temperature compensation is achieved through a first and a second voltage divider each comprising a diode detector, the output signals U_X, U_R from the voltage dividers being fed to two amplifiers with different gains and then further on to a differential amplifier;

said differential amplifier subtracting one signal from the other (U_X -U_R), so that the temperature dependence of the two signals U_X, U_R cancel out.

13. Surveillance system according to claim 1, wherein the sensor means comprises a non-magnetic, non-electrically conductive protection layer for protection of the magnetoelastic material.

14. Surveillance system according to claim 1, wherein the coil system of at least two sensing devices via a multiplexing unit are connected to an electronic system which alternatively comprises a computer unit or is connected to an external computer unit or that the result of each sensor means can be observed separately.

15. Surveillance system according to claim 1, wherein the sensor system is provided with a shielding structure for protection of the sensor system when mounted externally.

16. Surveillance system according to claim 1, wherein each sensor system comprises separate demodulating electronics.

17. Use of a surveillance system as claimed in claim 1 in slewing rings.

18. A surveillance system for measuring stress on a fastener having a securing means, comprising:

a sensor comprised of a magnetoelastic material;

a sensing device comprising a coil system for exciting said magnetoelastic material, said sensing device at least partly surrounding said sensor;

means for arranging said sensor on said fastener between an object being fastened and said securing means such that said sensor is sensitive to compressive forces created between said securing means and said object when a load is placed on said object by said securing means; and

an electronic system connected to said sensing device for monitoring loads sensed by said sensor.

19. The surveillance system of claim 18, wherein said sensing device is set so as to excite said sensor predominantly by a small angle magnetization rotation process.

20. The surveillance system of claim 18, wherein said arranging means retains said sensor on said fastener such that said sensor is compressed between said securing means and said object when a load is placed on said object by said securing means.

21. The surveillance system of claim 18, wherein said sensor is annular and surrounds said fastener.

22. The surveillance system of claim 18, wherein said magnetoelastic material is excited with a frequency of at least 300 kHz.

23. The surveillance system of claim 18, wherein said magnetoelastic material is excited with a frequency between 500 kHz and 10 MHz.

24. The surveillance system of claim 18, wherein said magnetoelastic material is a magnetoelastic amorphous material.

25. The surveillance system of claim 18, wherein said magnetoelastic material is applied axially on said sensor.

26. The surveillance system of claim 18, wherein said magnetoelastic material comprises magnetoelastic ribbons in the form of a ribbon belt.

27. The surveillance system of claim 18, wherein said sensor comprises a washer.

28. The surveillance system of claim 18, wherein said coil system completely encloses said sensor.

29. The surveillance system of claim 18, wherein said coil system comprises coils for carrying out both an excitation function and a pick-up function.

30. The surveillance system of claim 18, wherein said sensing device includes temperature sensing means and temperature compensation means.

31. The surveillance system of claim 18, wherein said sensing device includes temperature sensing means and temperature compensation means.

32. The surveillance system of claim 31, wherein said temperature sensing means includes a conventional Resistance Temperature Detector attached to the fastener and the temperature compensation means includes an electric feedback loop.

33. The surveillance system of claim 18, wherein said sensor comprises a nonmagnetic, nonelectrically conductive protection layer for protecting the magnetoelastic material.

34. The surveillance system of claim 18, wherein said system includes a plurality of sensors and sensing devices and the electronic system includes means for observing each sensor separately.

35. A method of monitoring stress on a fastener having a securing means, comprising:

arranging a sensor comprised of a magnetoelastic material on said fastener between an object being fastened and said securing means such that said sensor is sensitive to compressive forces created between said securing means and said object when a load is placed on said object by said securing means;

at least partly surrounding said sensor with a sensing device comprising a coil system for exciting said magnetoelastic material; and

connecting an electronic system to said sensing device for monitoring loads sensed by said sensor.

36. The method of claim 35, further comprising the step of exciting said sensor predominantly with a small angle magnetization process.

37. The method of claim 35, wherein said magnetoelastic material is excited with a frequency of at least 300 kHz.

38. The method of claim 35, wherein said magnetoelastic material is excited with a frequency between 500 kHz and 10 MHz.

39. The method of claim 35, wherein said magnetoelastic material is excited with a frequency between 500 kHz and 10 MHz.