SENSOR MOUNTING PAD WITH SECONDARY RESTRAINT FEATURE

Abstract

A device and method for mounting sensors to components comprising a mounting pad adapted for adhesive attachment to the component and further including a feature allowing for a secondary restraint. In various variations, the sensor may be an accelerometer, vibration sensor, temperature sensor or other sensor. The feature and secondary restraint may include one or more holes in the mounting pad for attachment by safety wire or other restraint to provide limited movement in the case of adhesive failure.

Claims

1. A mounting pad for attachment of a sensor to a component for an analysis, said mounting pad comprising: a block having a first surface prepared for adhesive mounting of said block to said component; said block having a second surface for receiving attachment of said sensor to said block, said block having a feature for attachment of said sensor to said block; said block having a safety feature for coupling to a safety restraint to limit movement of said block in an event of an adhesive failure of said adhesive attachment.

2. The mounting pad as recited in claim 1, wherein said sensor is a vibration sensor and said analysis is a vibration analysis.

3. The mounting pad as recited in claim 1, wherein said feature for attachment comprises said block having a threaded hole for threaded attachment of said sensor to said block; said threaded hole having an opening on said second surface.

4. The mounting pad as recited in claim 3, wherein said threaded hole is a threaded through hole through said block with neither opening on said first surface.

5. The mounting pad as recited in claim 3, wherein said threaded hole is a threaded blind hole with a closed bottom.

6. The mounting pad as recited in claim 1, wherein said safety feature comprises a hole through said block with openings not fully obscured by said component or said sensor when attached to said component and said sensor; and said safety restraint comprises a safety wire.

7. The mounting pad as recited in claim 1, further comprising said block having a counter torque feature adapted for coupling to a tool for applying counter torque to counteract torque applied while mounting or unmounting said sensor using said feature for attachment of said sensor to said block.

8. The mounting pad as recited in claim 7, wherein said counter torque feature comprises a hole into and not completely through said block and not perpendicular to said second surface.

9. The mounting pad as recited in claim 7, wherein said counter torque feature comprises two parallel flat surfaces perpendicular to said second surface adapted for use with a wrench for applying said counter torque.

10. The mounting pad as recited in claim 9, wherein said block is hexagonal and said two parallel flat surfaces are two faces of said hexagonal block.

11. The mounting pad as recited in claim 1, wherein said second surface is parallel to said first surface.

12. The mounting pad as recited in claim 1, wherein said second surface is perpendicular to said first surface.

13. The mounting pad as recited in claim 1, wherein said first surface has a pattern to improve adhesive bonding.

14. The mounting pad as recited in claim 13, wherein said pattern comprises groove cutouts.

15. The mounting pad as recited in claim 1, wherein said first surface has a chemical treatment to improve adhesive bonding.

16. A method for mounting a sensor on a device comprising steps in no particular order: forming a mounting pad block for mounting said sensor on said device; forming a mounting surface on said block; adapting said mounting surface for adhesively mounting said block to said device; forming a second surface on said block; forming a feature for fastening of said sensor on said second surface; forming a through hole in said block, said through hole not penetrating said mounting surface; adhesively mounting said block on said device; threading a safety wire through said through hole and attaching said safety wire to said device; and mounting said sensor on said block by using said feature for fastening of said sensor on said second surface.

17. The method in accordance with claim 16, wherein said feature for fastening is a threaded hole in said block, said threaded hole having an opening on said second surface and not having an opening on said mounting surface; and said mounting of said sensor comprises using a threaded fastener with said threaded hole in said block and applying torque to said threaded fastener to secure said sensor on said block.

18. The method in accordance with claim 17, further including forming a counter torque feature in said block; and applying opposite torque to said block using said counter torque feature while applying torque to said threaded fastener to secure said sensor on said block.

19. The method in accordance with claim 18, wherein said counter torque feature comprises a hole formed in said block.

20. The method in accordance with claim 18, wherein said counter torque feature comprises parallel flat surfaces adapted for coupling to a wrench.

21. The method in accordance with claim 20, wherein said block is hexagonal and said counter torque feature is two faces of said hexagonal block.

22. The method in accordance with claim 16, wherein said second surface is parallel to said mounting surface.

23. The method in accordance with claim 16, wherein said second surface is perpendicular to said mounting surface.

24. The method in accordance with claim 16, further including applying a pattern to said mounting surface to improve adhesive bonding.

25. The method in accordance with claim 24, wherein said pattern comprises groove cutouts.

26. The method in accordance with claim 16, further including applying a chemical treatment said mounting surface to improve adhesive bonding.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0029] The present invention is described with reference to the accompanying drawings. In the drawings, like reference numbers indicate identical or functionally similar elements.

[0030] FIG. 1 shows a perspective view of an exemplary mounting pad adapted for secondary restraint.

[0031] FIG. 2 displays a top view of the mounting pad of FIG. 1.

[0032] FIG. 3 shows a bottom view of the mounting pad of FIG. 1.

[0033] FIG. 4 shows a perspective view of an exemplary 90 degree mounting pad with a safety wire hole.

[0034] FIG. 5 shows a top view of the exemplary 90 degree mounting pad.

[0035] FIG. 6 shows a bottom view of the exemplary 90 degree mounting pad.

[0036] FIG. 7 shows an exploded view of the exemplary mounting pad with a mounting screw, washer, and accelerometer.

[0037] FIG. 8 shows an exploded view of the exemplary 90 degree mounting pad with a mounting screw, washer, and accelerometer.

[0038] FIG. 9 is a perspective view of an alternative embodiment of a mounting pad with flat sides and two safety wire holes.

[0039] FIG. 10 is a top view of the alternative embodiment of FIG. 9.

DETAILED DESCRIPTION

Mechanical Fasteners

[0040] Traditionally, accelerometers have been mounted by way of mechanical fasteners such as bolts or screws. Advantages include secure, high strength, reliable fastening with ease of removal and replacement. However, in some applications such as vehicle health monitoring, there are very few locations where a bolted connection is possible. Gearboxes, engines, and transmission casings often cannot be drilled and tapped for a threaded sensor installation in an aftermarket installation where the installation was not designed in from the start. The desired location may not be possible either because of practical reasons or regulatory/certification reasons. Practically, the strength of the material may not support the cutting of threads to sufficient strength to enable a bolted connection, or the material may not have enough depth to allow a sufficient number of threads. Further, regulatory or certification agencies can also prohibit the modification of transmissions, gearboxes, or engines to facilitate sensor installation. Often, the only choice in mounting locations is where a mechanical fastener already exists, or a pre-threaded location.

[0041] Further, structural vibration modes may dictate the optimal or necessary location, and that location may not have available existing attachment points. In vibration monitoring, not all locations on a component transmit vibration equally. On any component, there are both nodes where vibration displacement is greatest, and antinodes where displacement is minimal or near zero. In determining where to instrument a component for vibration monitoring, it is important to locate the accelerometer near a node. This is done by resonance testing using special equipment. Pre-threaded or existing hardware locations may occasionally coincide with a vibration node, but often this is not the case.

Adhesive Mounting

[0042] By mounting accelerometers adhesively to the component of interest rather than using a bolt or screw, several advantages may be realized, including but not limited to: the location may be less limited, a smaller size may be possible, and fewer sensors may be needed. Location less limited—adhesive mounting of the accelerometer possibly enables a location to be selected that coincides much closer with a vibration node. This removes the constraint to mount the sensor at a predefined location. Subject to practical considerations such as excessive temperature or mechanical interference from moving parts, the sensor may be mounted anywhere on the component of interest that will enable the best measurement of vibration.

[0043] Smaller size possible—the size of the accelerometer is no longer constrained by the dimension of an existing hardware size, and can typically be made much smaller. A smaller, lighter accelerometer changes the vibration characteristics of the component less, an effect known as mass loading. A lighter accelerometer is also an advantage for applications such as aircraft where higher weight negatively affects overall system capability.

[0044] Fewer sensors needed—with few or no constraints on mounting location, adhesive mounted sensors can be placed in optimal locations for monitoring multiple internal subcomponents on a gearbox, transmission, or engine. On large or complex assemblies, it is often necessary to monitor multiple bearings or gears. When limited to pre-existing mounting locations, it frequently becomes necessary to place more sensors than would otherwise be required if optimal locations could have been selected. Using an adhesive mounted approach, an engineer can perform an optimization to select a location having a transfer path to monitor all components of interest and eliminating superfluous sensors.

Safety Concerns If the Adhesive Fails

[0045] The failure of adhesively mounted sensors in a critical environment, such as on an aircraft, can have disastrous consequences. On an aircraft, the sensor and cable can interfere with critical engine or flight controls if they become dislodged. Very strong adhesives do exist which should prevent the sensor from coming loose; however, the uncontrolled environment in which they are applied can significantly reduce adhesive strength. Improper surface preparation or degreasing can result in a very weak bond. Too short a cure time before resumption of operation may also weaken the bond. Regulatory agencies responsible for aircraft/vehicle safety certification have been hesitant to approve adhesively mounted accelerometers because of the serious impact should they become disbonded.

Maintenance Challenges

[0046] Removal of the sensors may be required during the course of maintenance operations, either to replace the sensor or to facilitate maintenance of another device. An adhesively mounted sensor presents difficulties when it must be removed to facilitate maintenance. Gearboxes, transmissions, and engines must on occasion be removed or replaced, and any accelerometer mounted on the old component must be transferred to the newly installed component. Adhesively mounted accelerometers and protective finishes can easily be damaged during removal, since the bond must be either mechanically broken with force, or chemically dissolved with a solvent. Removing and re-attaching an adhesive mounted sensor significantly increases the maintenance burden of replacing the component to which it is attached.

Mounting Pad

[0047] In one variation, the sensor may be mounted on a mounting pad (alternatively referred to as a base) such that an accelerometer is attached by way of threaded hardware to a base, and the base is adhesively mounted on the object to be monitored. It is then possible to remove the accelerometer while leaving the base permanently attached. This will facilitate maintenance or accelerometer replacement without the need to break the adhesive bond.

[0048] Although adhesive bonded mounting pads are widely used in non-critical settings for accelerometers, they are not used in critical settings such as onboard aircraft. The likelihood of the base becoming disbonded is similar to the likelihood of a directly adhered accelerometer becoming disbonded. Should the adhesive fail, there is significant risk that the accelerometer, cable, and/or mounting pad could cause grave damage.

[0049] The adhesively bonded mounting pad may include attachment features, for example holes for safety wire or tapped holes for looped fasteners for safety wire or other flexible restraint that may be affixed to an appropriate bolt or other feature in the aircraft to prevent unlimited and hazardous free movement of the accelerometer should the adhesive bond fail.

[0050] During installation, the mounting pad is adhesively affixed to the desired position on the device. The safety wire may be threaded through the mounting pad safety wire hole or other feature and affixed to an anchor point on the equipment. In one variation, the anchor point may be on the same structure, potentially allowing the safety wire to remain in place even though the accelerometer may be removed during maintenance, depending on the circumstances.

[0051] The mounting pad may further include torque limiting features to reduce torque on the adhesive attachment during installation and removal of the sensor. The sensor may be mounted to the mounting pad by one or more bolts or other threaded attachments. The threaded attachments may require torque to install or remove the sensor. The mounting torque may potentially damage or debond the adhesive attachment layer.

[0052] The mounting pad may include a torsional restraint feature such as a hole, a notch, or flat sides that can be used to apply counter-torque to the pad while a sensor is affixed to the mounting pad with a threaded fastener or while such a sensor is removed. Applying torque to the sensor bolt while simultaneously applying torque of similar magnitude and opposite direction (counter-torque) to the mounting pad may result in greatly reduced or near zero torque applied to the adhesive bond, thereby reducing the likelihood that the adhesive bond will fail or be damaged during sensor installation or removal.

[0053] Use of the torsional restraint feature may require the use of a torsional restraint tool such as a pin, a hex wrench, any of various plyers, any of various wrenches, a specially designed tool, or another tool. The tool may be inserted into a hole or notch in the mounting pad body, mated with wrench flats on the outer edges of the mounting pad body, and/or mated with an alternative restraint feature in or on the mounting pad. As the sensor is being secured to the mounting pad using tightening torque, counter-torque can be applied in the opposite direction of the tightening torque by the torsional restraint tool to reduce the torsional shear stress applied to the adhesive from the tightening torque applied to the sensor fastener. The torsional restraint feature can also be used to apply counter-torque in the opposite direction of the loosening torque when removing the sensor fastener from the mounting pad to reduce the torsional shear stress applied to the adhesive from the loosening torque applied to the sensor fastener.

[0054] FIG. 1 shows a perspective view of an exemplary mounting pad adapted for secondary restraint. The mounting pad 1 may have a circular base typically 0.125 inch to 1 inch (3 to 25 millimeters) diameter while retaining a relatively small thickness, for example, but not limited to 3 to 5 millimeters (0.125 inch to 0.200 inch.) The mounting pad (also referred to as a block) may comprise medium carbon steel rod with corrosion resistant coating for good strength, toughness, and wear resistance. However, other materials may be used, as needed.

[0055] The bottom surface (not visible in FIG. 1, but opposite and typically parallel to top surface 5) may be typically nominally flat, but may be conformal to a desired surface of a particular installation. The bottom surface may be textured or may be treated by etching or priming or other treatment for optimal adhesion of a desired adhesive system.

[0056] The top mounting surface 5 may be perpendicular to the curved surface edges of mounting pad 1, and the top surface 5 may have a smooth machine finish. The accelerometer mounting hole 4 (recess 4) is typically partially threaded, located at the center of surface 5, and preferably does not completely pass through the body (thickness) of the mounting pad 1. The mounting hole 4 extending partially through the thickness, i.e., closed on the bottom end, prevents a mounting screw from inadvertently pushing through, lifting the mounting pad 1, and delaminating the adhesive mounting. Further, the blocked end of the mounting hole 4 prevents adhesive from filling the mounting hole 4. Located on the curved surface edges of the mounting pad 1 is a torsional restraint hole 2 which may be unthreaded and centered vertically with the height of the mounting pad 1. FIG. 1 shows safety wire hole 3. One or more safety wire holes may be provided. Safety wire hole 3 opposite torsional restraint hole 2 passes completely through mounting pad 1, and may be centered vertically with the height of the mounting pad 1 with an axis parallel to the bottom or top surface 5. A safety wire, not shown, may be threaded through the hole and tied or otherwise connected to nearby structure to prevent potentially hazardous movement of the mounting pad and sensor in the event of an adhesive bond failure. The safety wire may be any metallic, plastic, fiber or other string, chord or wire of one or more strands, collectively referred to as “safety wire” in this disclosure.

[0057] FIG. 2 displays a top view of the mounting pad of FIG. 1 with hidden lines shown for clarity. The torsional restraint hole 2 is parallel with the top surface, and has a depth that does not obstruct the accelerometer mounting hole 4. Note that the safety wire hole 3 is completely through the mounting pad 1 and is opposite and perpendicular to the torsional restraint hole 2. Observe that both the torsional restraint hole 2 and the safety wire hole 3 have centerlines that are perpendicular to one another.

[0058] FIG. 3 is a bottom view of the mounting pad of FIG. 1 showing circular cuts into the bottom surface that are very small in depth and width at locations 6 and 7. Note these cut outs are located on the same plane offset into the body of mounting pad 1 away from the surfaces at locations 8, 9, and 10. The bottom surfaces of mounting pad 1 are typically not smoothly machine finished, leaving a texturized adhesion surface. The groove cutouts help with the adhesion and lateral strength of an adhesive. Other groove patterns including radial and mesh patterns may be used. In addition, chemical etching or primers may be applied to prepare for the adhesive. In a further alternative, the bottom surface contour may be conformal to a desired installation, for example, but not limited to a spherical or cylindrical curvature. For this disclosure, the term flat or substantially flat referring to the adhesive bond surface may include surfaces having texture or patterns for improving adhesive bond strength. Parallel to the adhesive bond surface would be parallel to a plane through an average surface, averaging out the texture. Note that hole 4 of FIG. 2 is not shown because hole 4 does not penetrate the bottom surface shown in FIG. 3.

[0059] FIG. 4 shows a perspective view of an exemplary alternative variation for a 90 degree mounting pad. The 90 degree mounting pad 11 may have a circular base typically 3 to 25 mm, 0.125 in to 1 in., with an increased height larger than the FIG. 1 embodiment 1 usually in a range from 8 to 25 mm, 0.35 in to 1 in. The 90 degree mounting pad 11 may comprise a medium carbon steel rod with corrosion resistant coating for good strength, toughness, and wear resistance. However, other materials may be used. The vertical mounting surface 26 is rotated 90 degrees from the FIG. 1 top mounting surface 5, and may comprise a smooth machine finish as desired for mounting an accelerometer. Surface 25 is parallel to the top surface 27. A longitudinal cut out from surface 25 moving up to surface 27 has been removed from the embodiment of mounting pad 11, and the remaining surface after removal of material is surface 26. Accelerometer threaded mounting hole 14 is centered vertically and horizontally on mounting surface 26 with one or more safety wire holes 12 and 13 located, for example in the bottom left and right corners.

[0060] FIG. 5 displays a top view of the exemplary 90 degree mounting pad 11 with hidden lines shown for clarity. The two safety wire holes 12 and 13 are through-holes in the mounting pad embodiment 11 displayed as hidden lines. The accelerometer mounting hole 14 is threaded and may not completely pass through the exemplary mounting pad embodiment 11. Note holes 12, 13, and 14 have centerlines that are parallel.

[0061] FIG. 6 shows a bottom view of the exemplary 90 degree mounting pad 11 showing circular cuts into the bottom surface that are very small in depth and width at locations 16 and 18. Note these cut outs are located on the same plane and offset into the body of mounting pad 1 away from the surfaces at locations 15, 17, and 19. The bottom surfaces of mounting pad 1 are unfinished or prepared for adhesive leaving a rough texturized adhesion surface.

[0062] FIG. 7 shows an exploded view of exemplary mounting pad 1 with mounting screw 24, washer 22, and accelerometer 20. The mounting screw 24 feeds through center holes of the washer 22 and accelerometer 20 at locations 23 and 21, and threads into the accelerometer mounting hole 4. When fastened, the bottom face of the accelerometer 20 will be coincident with the top surface 5 of the mounting pad, and the bottom surface of washer 22 will be coincident with the top surface of accelerometer 20. Safety wire feasibly can be fed through safety wire hole 3 in a typical use case.

[0063] FIG. 8 shows an exploded view of the 90 degree mounting pad 11 with mounting screw 24, washer 22, and accelerometer 20. The mounting screw 24 feeds through center holes of the washer 22 and accelerometer 20 at locations 23 and 21, and threads into the accelerometer mounting hole 14. When fastened, the bottom face of the accelerometer 20 will be coincident with the vertical mounting surface 26 (FIG. 4) of the mounting pad 11, and the bottom surface of washer 22 with be coincident with the top surface of accelerometer 20. Safety wire feasibly can be fed through safety wire hole 12 and 13 in a typical use case.

[0064] FIG. 9 illustrates an alternative exemplary embodiment of a flat mounting pad 41 with flat sides 42, a safety wire hole 3, and a second safety wire hole 43. The flat sides 42, typically in opposing parallel pairs, may be separated by a distance (width) typically 3 mm to 25 mm, 0.125 inch to 1 inch and may be arranged suitable of use with a wrench, socket, or similar tool. Other features and attributes are illustrated based on the features of the mounting pad 1 shown in FIG. 1 and FIG. 2.

[0065] FIG. 10 illustrates a top view of the exemplary mounting pad 41 of FIG. 9. Note that the safety wire hole 3 and the second safety wire hole 43 are completely through the mounting pad 41, parallel with each other, and parallel with the top mounting surface 5.

Applications

[0066] The present disclosure is well adapted to affixing accelerometers to aircraft components for vibration health monitoring (VHM). The application, however, may extend generally to aircraft, automotive, rail, and marine applications as well as industrial machinery or other products using VHM. The application may further extend to other non-VHM uses where there is a need to securely affix various sensors to various components at locations not well suited to traditional mechanical fasteners.

Conclusion

[0067] While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.

DRAWING REFERENCE NUMERALS

1. Flat Mounting Pad Embodiment

2. Torsional Restraint Hole

3. Safety Wire Hole of Flat Mounting Pad

4. Accelerometer Mounting Hole of Flat Mounting Pad

5. Top Surface of Flat Mounting Pad

6. Outer Bottom Cutout Groove of Flat Mounting Pad

7. Inner Bottom Cutout Groove of Flat Mounting Pad

8. Outer Bottom Contact Surface of Flat Mounting Pad

9. Middle Bottom Contact Surface of Flat Mounting Pad

10. Center Bottom Contact Surface of Flat Mounting Pad

11. 90 Degree Mounting Pad Embodiment

12. Right Safety Wire Hole of 90 Degree Mounting Pad

13. Left Safety Wire Hole of 90 Degree Mounting Pad

14. Accelerometer Mounting Hole of 90 Degree Mounting Pad

15. Outer Bottom Contact Surface of 90 Degree Mounting Pad

16. Outer Bottom Cutout Groove of 90 Degree Mounting Pad

17. Middle Bottom Contact Surface of 90 Degree Mounting Pad

18. Inner Bottom Cutout Groove of 90 Degree Mounting Pad

19. Center Bottom Contact Surface of 90 Degree Mounting Pad

20. Accelerometer

21. Accelerometer Through-Hole

22. Washer

23. Washer Through-Hole

24. Screw

25. Lower Horizontal Surface of 90 Degree Mounting Pad

26. Vertical Mounting Surface of 90 Degree Mounting Pad

27. Top Horizontal Surface of 90 Degree Mounting Pad

41. Alternative Flat Mounting Pad Embodiment

42. Torsional Restraint Surface

43. Second Safety Wire Hole