Compound optical coupler and support mechanism

A support mechanism for protecting an object is described. The support system includes at least one support ring for providing dynamic protection to the object. One embodiment includes a support ring having corrugated bumps. Another embodiment includes multiple support rings axially separated by spacers. A compound optical coupler is also described, which has a self-wetting clear optical coupling gel and an elastomeric load ring.

BACKGROUND

The invention generally relates to a protective mechanism and an optical coupler for use in systems for detecting the presence of hydrocarbons during mining or drilling operations. In the prior art, special optical couplers using Sylgard along with optical coupling oil have been employed with prior support systems to couple light from a scintillation element into a light detector device. Such an optical coupler is disclosed in U.S. Pat. No. 6,465,788, which is incorporated herein by reference in its entirety. One drawback to this approach is that, under some extreme cases of high loads, uneven loads, or high vibration, oil used in the optical coupling may migrate out over time and result in degraded detector performance. Another drawback is that precision fabrication and/or assembly tolerances must be maintained to prevent loss of oil and degraded performance. Yet another drawback is that particulate contamination of the optical coupler can also cause loss of oil and degraded performance.

Optical couplers made from self-wetting type materials (e.g., Wacker) have also been used. A drawback to these concepts is that the self-wetting materials exhibit viscous behavior and tend to flow outward from the optical interface, allowing the optical interface retaining force to be lost, and thus resulting in degraded performance.

Nuclear detectors, such as gamma detectors, have been used in mining applications and oil drilling operations for many years. In particular, gamma detectors have been used to measure the radiation that emanates from the formations surrounding the mining or drilling equipment. Such gamma detectors operate by utilizing the differences between the natural radioactivity of the target formation and the natural radioactivity of the adjacent formations to determine the boundaries between these formations.

Gamma detectors are sensitive and must be protected from harsh environments to survive and to produce accurate, noise free signals. This protection must include protection from physical shock and stress, including force, vibration, and abrasion, encountered during solid mineral mining and oil drilling operations. However, the closer in proximity the gamma detector is to the mineral being mined or drilled, the greater is the shock, vibration and stress to which the detector is subjected.

The presence of armor, which is required to protect the detector, further limits the available space. An explosion-proof housing takes up even more of the available space, and often results in reducing the diameter of the photomultiplier tube. When light detecting devices of relatively low mass density are used in connection with scintillation elements having a relatively high mass density, a specials means of support is needed to reduce rotation moments when under high vibration or high shock. Lower cost for providing protection for the detector is also needed.

A support system must be very effective in protecting the detector from the harsh vibrations and shock, but must also do so while consuming a small amount of space. Similarly, in mining operations, the outer portions of the detector and the armor must provide a high level of shielding from unwanted radiation and must protect the detector from impact and abrasion, all with a minimal use of space.

In the prior art, detectors have been protected by a plurality of springs which extended along the axial length of the detector or its scintillation element. An example of such a support system is a flexible dynamic housing, as disclosed in U.S. Pat. No. 6,452,163, which is incorporated by reference herein in its entirety. One drawback of such systems is that the springs extend along the axial length of the scintillation element and as such can block radiation from reaching the scintillation element. Another drawback is that such a mechanism uses a plurality of parts around the circumference of the detector. Moreover, the springs of the flexible housing have to be custom made for this specific industrial application. Also the annular gap that exists between the scintillation element and its rigid housing is not always uniform, such as because of dimensions of tolerance. This may complicate the installation or sizing of the system. Moreover, if the gap is not uniform, the dynamics of the system along the length may not be uniform or may be affected.

Another support mechanism for a detector is disclosed in pending application Ser. No. 10/270,148, which is incorporated herein by reference in its entirety. This type of support mechanism is a flexible support sleeve which extends along the length of the detector or scintillation element, and suffers from the same drawbacks discussed above with respect to the springs.

There remains a need for an optical coupling system that is less sensitive to fabrication/assembly tolerances, high/uneven loads, and high vibrations. There is also a need for a simplified, lower cost structure and method for supporting instrumentation packages and sensors, such as gamma detectors. A means for supporting sensitive elements, which have substantially a cylindrical shape, is needed to work in cooperation with other suitably chosen support elements. A more suitable method of supporting sensitive elements so as to produce less compression of optical reflecting material is also needed.

SUMMARY

The inventions provide a gamma detector which, in some aspects, may be utilized in oil well drilling and/or servicing operations, and solid mineral mining operations. In one aspect of the inventions, the gamma detector includes a scintillation element.

In one aspect, the invention provides a scintillation element package comprising a scintillation element; a housing encompassing the scintillation element; and a support mechanism including at least one support ring, the support mechanism being between the scintillation element and the housing.

In another aspect, the invention provides a gamma detector comprising: a photomultiplier tube; a first housing surrounding the photomultiplier tube; and a support mechanism including at least one support ring supporting the photomultiplier tube.

In yet another aspect, the invention provides a support mechanism comprising: a rigid housing and a support mechanism having a support ring, wherein the support mechanism at least partially surrounds an object to be protected, and wherein the support mechanism is between the rigid housing and the object.

In still another aspect, the invention provides a detector comprising: a scintillation element; a first housing and a second housing; an inner support mechanism including at least one support ring, said inner support mechanism supporting the scintillation element; an outer support mechanism including at least one support ring, said outer support mechanism supporting the scintillation element and surrounding said inner support system.

In another aspect, the invention provides a compound optical coupling assembly comprising a self-wetting optical coupling gel in an interior portion of the optical coupling assembly, and an elastomeric load ring radially outward of the self wetting optical coupling gel.

This invention provides a low cost method of supporting instrumentation systems and/or subsystems within mining equipment, or other equipment used in harsh environments. The invention provides a scintillation element package that includes a scintillation element, a shield encompassing the scintillation element, and a support mechanism having a support ring at least partially surrounding the scintillation element within the shield, the support mechanism providing support for the scintillation element.

The invention also provides, in one aspect, a support mechanism that includes a support ring surrounding and protecting an object to be protected, wherein the support mechanism provides support for the object. In another aspect, the invention provides a support mechanism having a support ring including an inner support mechanism surrounding and protecting an object to be protected and an outer support mechanism surrounding the inner support mechanism, the outer support mechanism fitting within a cavity.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1illustrates a gamma detector20installed into armor70for mounting a mining module for use in solid mineral mining operations. As shown inFIG. 1, the detector20is protected by armor70that surrounds, shields, and supports the detector. The detector20also may be used in conjunction with oilfield operations, without the armor70.FIG. 2shows a cross-sectional view of the gamma detector20.FIGS. 3 and 4, which are cross-sectional views ofFIG. 2, show the various components that protect the scintillation element50, the electronics57and other sensors. These multiple levels of protection are described in detail below.

With reference toFIGS. 1 and 2, gamma rays28entering the gamma detector20pass through a non-metallic window71to reach the scintillation element50within the detector20. Other windows65(FIG. 3) have been cut into a rigid dynamic enclosure80which surrounds the scintillation element50.

Next, with reference toFIG. 2, the general function of the detector20will be described. A scintillation element50responds to gamma rays28that have been emitted from rocks in the soil. The response of element50is to produce a tiny pulse of light that travels to a window52at the window end of the scintillation element50or is reflected into the window52by a reflector67(FIG. 3) that is wrapped around the scintillation element50. The light pulse travels through a first optical coupler51, through the window52, and through a second optical coupler53into the faceplate of a light detecting element, shown here as a photo-multiplier tube55. An electrical pulse is generated by the photo-multiplier tube55and sent to electronics element57.

The photo-multiplier tube55, the electronics element57and an accelerometer60are located in an assembly called a photo-metric module58. Since components within the photo-metric module58utilize electricity, it is necessary that it be enclosed in an explosion-proof housing59to avoid accidental ignition of gas or dust that may be in the vicinity of the detector20. Also, the explosion-proof housing59serves as an effective barrier that protects the electrical elements57and the accelerometer60from the strong electromagnetic fields generated by heavy electrical equipment.

Better details of the protective elements are shown inFIGS. 3 and 4. The first view inFIG. 3shows a support mechanism100that surrounds the scintillation element50, and protects it from high levels of lower frequency vibrations. The support mechanism100will be described in greater detail below. The support mechanism100between the scintillation element50and the scintillation shield63supports the fragile scintillation element50and provides a high resonant frequency so that it will not resonate with lower frequency vibrations that pass through the outer housing. The outer housing82encloses another support mechanism100, the rigid enclosure80and a rigid elastomeric shock absorbing sheath81which surrounds the enclosure80.

A typical size scintillation element50for this application is 1.4 inches in diameter by 10 inches in length, but may be as large as 2 inches in diameter. The resonant frequency of these outer support elements81,80protect against shock and isolate the scintillation element50from high frequencies.

FIG. 4illustrates a view of a photo-metric module including a photo-multiplier tube55inside a first housing58, which is within the explosion-proof housing59. The support mechanism100is located at three radial elevations about the photo-multiplier tube55: between the photomultiplier tube55and the first housing58; between the first housing58and the explosion-proof housing59; and between the explosion-proof housing59and the rigid enclosure80.

The elastomeric shock-absorbing sheath81fully covers the entire rigid dynamic enclosure80. It should be noted that this sheath81serves other useful purposes. It provides good mechanical compliance with the armor70. This is particularly important during installation in which dust and particles will be present. Another purpose of the sheath81is to prevent water or dust from entering through the window in the enclosure80. The accelerometer module60is afforded the same critical protection from the harsh environment as the photo-multiplier tube55.

In use, there is a need to firmly hold the light collecting element, which in this case is the photo-multiplier tube55, so that it remains fixed in position relative to the window52through which the light is passing from the gamma detector scintillation element50. This is especially important in the disclosed embodiment because the exemplary optical coupling between the photo-multiplier tube55and the window52is a two-piece compound coupling. One piece of the coupling is a soft, self-wetting pad typically made from a material called Wacker. Surrounding this inner coupling is a ring made from a more substantial material such as Sylgard, also pliable, optically transparent material. The self-wetting optical coupler of the invention will be discussed in greater detail below.

To work properly, the photo-multiplier tube55must not be free to move more than a few thousands of an inch in the radial direction, while at the same time, be pushed with a uniform force against the coupling elements and by a spring. To accomplish these dual requirements, the photo-multiplier tube55must be sufficiently free to move in the longitudinal direction while having its motion in the radial direction significantly restrained. Moreover, thermal expansion must not interfere with the two requirements discussed above.

These requirements are accomplished by the support mechanism100of the present invention. The support mechanism100comprises support rings which are placed around the photo-multiplier tube55. The support mechanism100will be described with reference toFIGS. 5 and 6. A main component of the support structure100is a support ring102, an example of which is shown inFIG. 5. Such a support ring102is commonly referred to as a tolerance ring in several industrial applications. One manufacturer of such rings is USA Tolerance Rings in Pennington, N.J.

The tolerance, or support ring is a device that facilitates fitting of concentric cylindrical parts. The support ring102has corrugated bumps104which have a height112. The support ring102also has a height110and a diameter114, and may have a rim108. In the example shown, the corrugated bumps extend, or face, toward the center of the support ring102. The inward facing corrugated bumps104compress in proportion to torque or radial load for wider dimensional tolerance. The support ring102is not continuous, and has an opening103. In use, the opening103allows the support ring102to flex to accommodate different diameters, to move and to absorb shock and to thermally expand. In a preferred embodiment, a support ring with a part number of ANL-R8-9-S from USA Tolerance Rings can be used. Such a support ring has a diameter114of approximately 1.125 inches, a height110of approximately 0.313 inches, and a bump height112of approximately 0.25 inches. However, the heights110,112of the support ring102and bumps104, and other parameters, may be varied to accommodate design parameters.

The support ring100is a frictional fastener, capable of handling direct torque transfer, torque slip, axial retention, controlled collapse and radial loading between mating cylindrical components. It is a corrugated metal strip that acts as an interface between two mechanical objects, to secure one to the other by interference fit. The corrugated bumps104deflect and allow the support ring102to act like an elastic shim.

The number of the support rings102is chosen depending on the configuration of the photo-multiplier tube55. In an exemplary embodiment, between two and five support rings are used. With reference toFIG. 6, three support rings102are shown supporting the photo-multiplier tube55. The support rings102may be held in place by metal tape or a metal retainer, designated by numeral106. The metal tape106has an adhesive material on its inward facing surface. The metal tape, or retainer106, is installed about the housing120of the photo-multiplier tube55. The metal tape or retainer106also functions as a spacer to laterally separate the support rings102. The support rings102do not extend longitudinally along the photo-multiplier tube55. Rather, the support rings102extend around the circumference of the photo-multiplier tube55, and are spaced out in intervals along its length.

FIG. 7shows the scintillation element50, photo-multiplier tube55and electrical elements57supported by the support mechanism100. InFIG. 7, the support rings102are shown at different radial elevations with respect to the supported components50,55,57. The support rings102at different radial elevations do not have to be concentric and can be spaced apart along the length of the protected elements50,55,57.FIG. 8shows a close-up view of the support mechanism100. The support rings102are separated by the metal tape or retainer106. The support rings102do not extend axially along the length of the photo-multiplier tube55. Rather, the support rings102are spaced apart axially, and extend around the circumference of the photo-multiplier tube55.

If the first housing58, the tolerance rings102and the photo-multiplier tube housing120are of the same material, or material with equivalent thermal expansion coefficient, there will be very little differential expansion due to thermal changes. In applications where the vibration and shock are the most serious environmental challenges and thermal changes are not significant, the choice of materials may not be very significant. In applications such as down-hole drilling for oil and gas, careful attention must be paid to the selection of compatible materials to avoid significant thermal expansion.

It should be noted that in a preferred embodiment, the housing around the photo-multiplier tube55is rigidly connected to a crystal outer housing so that the crystal outer housing and the photo-multiplier tube55do not move relative to each other. Therefore, if the support rings102do not allow excessive motion in the radial direction of the photo-multiplier tube housing120relative to the first housing58, then the photo-multiplier tube55would be held sufficiently well relative to the window52of the housing and crystal package combination.

If the support rings102are made from soft materials, such as elastomers, then they would tend to have a low resonant frequency and a relatively high dynamic transmissibility. This is known to have undesirable consequences. If the rings are made from a rigid material such as solid steel, then the tolerances of all the mating parts would have to be made extremely precise to prevent the elements from being loose, and they would have to be installed in a tight tolerance condition. Yet, if the support rings102are tight and rigid, then any errors in tolerances would render the support rings102difficult or impossible to install without damaging the delicate instruments. Some instruments for harsh environments are known to be designed in just this manner, and are known to be costly to manufacture. The solution is to use support rings102that are made from a strong material, such as stainless steel, but configured such that the support rings102have some elastic properties.

In order to conserve valuable space within the detector or other similar tool, the support rings102need to be very thin. In use, unique design parameters for the support rings102are selected to meet particular requirements of the application for which the support rings102are used. Some of the particular requirements are as follows.

The overall thickness of the support rings102is selected to fill gaps and tolerances between two components, and selection of appropriate tolerance rings is made using vendor catalog data. Friction forces exerted by the support rings102must be sufficient to prevent relative longitudinal motion between two components due to vibration forces, while the size of the support rings102must remain small enough to allow ease of assembly. Examples of nominal friction forces are 40 pounds-force for a 1 inch×4 inch detector, and 125 pounds-force for a 2 inch×10 inch detector. Support ring102data, provided by vendors, includes: Torque; Capacity; Diametral Clearance; material thickness; and corrugation pitch. These and other parameters are used to determine the appropriate support ring characteristics.

Another consideration when selecting a support ring102is protection in a high vibration environment. This is achieved by a natural vibration frequency of the combination of the component and support ring. The natural vibration frequency should not adversely couple with the vibration loads of the environment. Vibration environments that must be protected against are typically in the 100–200 Hz range. Thus, support rings102would typically be designed to provide a natural vibration frequency greater than 300 Hz. Stiffness of the support ring is the key parameter used to control the natural vibration frequency. Support ring vendor catalogs typically provide data used to determine support ring stiffness.

Still another consideration is to provide adequate structural support to components in order to prevent structural failure due to damaging acceleration loads. Multiple support rings102may be used along the length to provide support as needed to reduce mechanical stress. Traditional stress analysis techniques are used to determine where and how many support rings are needed.

Use of the support rings102in the present invention results in a desirable support mechanism100. The support rings102can be selected and installed to provide resistance to movement in the longitudinal direction within acceptable limits while limiting the movement in the axial direction to a few thousands of an inch. Thus, the support system100comprising the support rings102protects optical coupling elements from excessive stress.

The present inventions offer several advantages, as follows. The inventions provide a lower cost method of supporting instrumentation packages and sensors using off-the-shelf commercial parts. The inventions provide a more convenient method of delivering stiff support to an undersized component fitted into a standard sized housing (i.e., filling of the gap and tolerance). Also, when two parts of a detector assembly (e.g., electronics and crystal elements) that have different diameters are assembled into a common housing, use of tolerance rings allows the parts to be assembled without using sleeves to increase the smaller diameter. Another desirable result is that a lesser amount of radiation is blocked from entering into the scintillation element.

Unlike flexible sleeves and flexible dynamic housings that must extend along the length of the scintillation element, the support mechanism100having support rings102supports only at two or more locations of the scintillation element. This is possible because of the relative high stiffness of the support ring102due to the curved shape of the bumps104. If the support ring102has a rim108, i.e., the bump104does not extend the full height110of the support ring102, the ring will be even stiffer. This improves optical performance of the scintillation element. Since tolerance rings support only at locations of the scintillation element, this leaves a significant portion of the reflective tape along the length of the scintillation element not compressed, and uncompressed reflective tape has superior optical performance.

In addition, the support mechanism having support rings102works well where the annular gap between the photo-multiplier tube and its rigid housing is not uniform. Because the support rings do not extend along the axial length of the photo-multiplier tube, variances in the gap dimension in one location will not affect the dynamics of the system in another location. Each support ring102acts independently of other support rings102.

It should be recognized that there are alternative methods of applying the compound coupler and support rings to a scintillation element. For example, one method is to use wraps of teflon and steel between the scintillation reflector67and the support rings102. The scintillation element50is wrapped with teflon tape to about 0.03 inches, uncompressed, or with approximately 0.015 inches thick sheet of skived teflon to serve as a reflector. A thin layer of stainless steel, ideally 0.002 inches to 0.005 inches thick, is then wrapped around the teflon reflector, with the joint of the stainless steel wrap positioned on the opposite side of the scintillation element50from the joint of the skived teflon sheet. The inside surface of the steel wrap can be coated white, or with a reflective material to provide additional reflection of any light that may pass through the teflon reflector. Support rings102are then placed around this assembly with tape or bonded material to hold the rings in place, similar to the way elements106inFIG. 8are used in the embodiment described earlier.

Another method is to wrap the reflector67, which is around the scintillation element50, with two layers of stainless steel, the inside surface of the inside layer of stainless steel being coated with a reflecting material. The two layers of stainless steel would be separated by an elastomeric material that is molded or bonded, in the form of ridges or strips, to the surface of one of the layers (similar to the ridges of sheath81inFIG. 3). This approach is low cost and reduces the compression forces due to the expansion of the scintillation element50during temperature changes so that the support rings102may be a stiffer configuration to make installation simpler.

The compound optical coupler of the invention will now described with reference toFIG. 9, which shows in greater detail the first optical coupler51, the window52and the optical coupler53ofFIG. 2. The invention provides a compound optical coupler that transmits light pulses from a scintillation element50into the light detector device (e.g., photomultiplier tube55). To accomplish this, the invention includes a self-wetting clear optical coupling gel202, which can be Wacker, for example, and a special elastomeric load ring204, which can be Sylgard, for example. Alternatively, the load ring204can comprise another rubber-type material.

The elastomeric load ring204is molded or otherwise attached to the face of the photomultiplier tube55and the window unit52to form an annular ring with an outer diameter that is preferably the same as that of photomultiplier tube55. The inner diameter of the load ring204is sized based on the forces that it must withstand. A self-wetting optical material is then poured into the inner diameter of the load ring204, forming a slightly convex surface. The convex surface allows for good contact with the self-wetting coupler material prior to engaging the elastomeric load ring204, thus providing a good optical interface.

The drawbacks associated with previous attempts to use a self-wetting clear material in an optical coupler are circumvented by the present invention which uses an elastomeric load ring204. The elastomeric load ring204made from an elastomeric material can be bonded, or otherwise attached to the light detector device (e.g., photomultiplier tube55) or to a window of a scintillation element50as an annular ring outside the primary light paths. The elastomeric load ring204serves as: (1) the primary load path to maintain the interface forces between the scintillation element50and the light detector device; and (2) as a retainer ring to prevent migration of the soft self-wetting clear material202from the interface. The result is an interface between the scintillation element50and light detector device that is self-healing, is pliable enough to maintain a clear bubble-free interface under extreme loads and vibration, and is more tolerant of fabrication and/or assembly tolerances.

While the invention has been described in detail in connection with preferred embodiments known at the time, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention.