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Description  |
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BACKGROUND OF THE INVENTION
This invention relates generally to computerized axial tomographic analysis
and, more particularly, to an apparatus for accurately positioning a
sample, such as a core sample from a borehole, to be scanned by a
computerized axial tomographic scanner.
SUMMARY OF THE INVENTION
In accordance with the present invention there is provided an apparatus for
positioning a sample in the radiation field of a computerized axial
tomographic scanner (hereinafter referred to as "CAT") for scanning by the
CAT. The subject apparatus comprises a first support means which is
positioned on a first side of the CAT and has a first guide means, a first
trolley means having means for engaging the first guide means, and means
for moving the first trolley means along the first guide means. A second
support means is positioned on a second side of the CAT, such second side
being opposite the first side of the CAT. The second support means has a
second guide means, and a second trolley means is provided with means for
engaging the second guide means. The first trolley means is coupled to the
second trolley means by a suitable coupling means such that movement of
the first trolley means causes similar movement of the second trolley
means with the coupling means passing through the radiation field of the
CAT. Holding means is attached to the coupling means for holding the
sample. Sample position sensing means and the moving means are connected
to means for controlling the position of the sample.
The present invention provides a system by which a sample, such as a core
sample from a borehole which is frozen or maintained at reservoir
conditions, can be easily and accurately positioned in the X-ray field of
a CAT. The system can be utilized to move the sample by a predetermined
amount so that scans can be taken at a plurality of points along the
sample to provide a detailed analysis along its longitudinal axis. In
addition, the system of the present invention can be utilized to
reposition the sample at a predetermined point in the event that it is
desired to perform additional analysis at that location. It should be
noted that the preferred embodiment described hereinbelow provides
repeatable positioning within 0.0001 inch.
In the preferred embodiments of the subject invention, similar support
structures are positioned on opposite sides of the CAT; these support
structures are provided with a set of rails and a trolley adapted to ride
on such rails. One of the support structures is provided with a motor and
gear which mates with appropriate threading on the trolley associated with
that support structure so that the trolley can be moved along the rails. A
tubular member which passes through the radiation field is attached to
both trolleys such that movement of the first trolley causes a similar
movement of the second trolley. Suitable sample holding means, such as a
pressurized sample holder for holding a core sample from a borehole, are
fixedly attached inside the tubular member.
Other objectives, advantages and applications of the present invention will
be made apparent by the following detailed description of the preferred
embodiments of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of a computerized axial tomographic sensor
utilizing the sample positioning system of the present invention.
FIG. 2 is a side view of the sample positioning system of the present
invention.
FIG. 3 is a cross sectional view taken along lines 3--3 of FIG. 2.
FIG. 4 is a top view of the motorized side of the sample positioning
system.
FIG. 5 is a cross sectional view taken along lines 5--5 of FIG. 2.
FIG. 6 is a side view of the tube and cylinder portion of the sample
positioning system.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIG. 1, a typical CAT employs an X-ray source 10 to provide
X-rays which are indicated by a plurality of arrows; these X-rays are
collimated by collimator 12 prior to passing through core sample 14. After
the X-rays have passed through core sample 14, they are filtered by filter
16 which can be, for example, air, tungsten or copper. Alternatively,
filter 16 can be applied to the X-rays prior to their entering core sample
14 rather than after their passage through core sample 14. The filtered
X-rays are then detected by X-ray detectors 18 which generate signals
indicative thereof; these signals are provided to suitable data processing
and recording equipment 20. The entire operation, from the generation of
the X-rays to the processing of the data is under the control of system
controller 22. Suitable signals are provided by system controller 22 to
voltage controller 24 which controls the voltage applied to X-ray source
10, thereby controlling the energy range of the X-rays. Alternatively,
filter 16 can be used to vary the energy range as is known in the art.
System controller 22 also provides suitable control signals to filter
controller 26 to apply the appropriate filter to the X-rays which have
passed through core sample 14 before they are detected by X-ray detector
18. The point along core sample 14 that is being analyzed is detected by
sample position sensor 28 which provides signals indicative thereof to
sample position controller 30. System controller 22 provides signals which
are indicative of the desired point along core sample 14 or the amount of
advancement from the last point analyzed, to sample position controller
30, which moves core sample 14 to the proper location.
Referring now to FIGS. 2-6, the preferred embodiment of the sample
positioning system of the present invention is shown in detail. A typical
CAT, for example, the Deltascan-100 manufactured by Technicare Corporation
of Cleveland, Ohio is indicated by numeral 34. CAT 34 has a gantry 36
which contains X-ray source 10, collimator 12, filter 16 and X-ray
detectors 18. Support structures or tables 38 and 40 are located on
opposite sides of CAT 34 and have legs 42 which are suitably attached to,
for example, the floor, to ensure that tables 38 and 40 maintain proper
positioning and alignment with CAT 34. Tables 38 and 40 each have a set of
guide means or rails 44, such as one inch diameter solid 60 case shafts
mounted on shaft support, Model No. SR-16, both being manufactured by
Thomson Industries, Inc. of Manhasset, N.Y., on which the legs 46 of
trolleys 48 and 50 ride. Preferably, legs 46 have a contact portion 47
that includes ball bearings in a nylon enclosure, such as the Ball Bushing
Pillow Block, Model No. PB0-16-0PN, which are also manufactured by
Thomson. Trolleys 48 and 50 have a flat member 52 which is attached to
legs 46 such that member 52 is parallel to rails 44. A member 54 which can
consist of two pieces fastened together by suitable means, such as screws,
is mounted on member 52 and has an aperture suitable for holding tube 56.
Member 52 of trolley 48 has a member 58 attached to the bottom portion of
member 52 that is provided with suitable screw threads for mating with
gear or screw 60. Screw 60 is driven by motor 62 for moving trolley 48
horizontally. Screw 60 can be, for example, a preloaded ball bearing
screw, Model No. R-0705-72-F-W, manufactured by Warner Electric Brake &
Clutch Company of Beloit, Wis., and motor 62 can be, for example, a DC
motor, Model No. 1165-01DCM0/E1000MB/X2, marketed by Aerotech, Inc. of
Pittsburgh, Pa. Motor 62 turns a predetermined number of degrees of
revolution in response to a signal from sample position controller 30 of
FIG. 1, which can be, for example, a Unidex Drive, Model No.
SA/SL/C/W/6020/DC-0/F/BR/R*, which is also marketed by Aerotech. Table 38
and trolley 48 also contain an optical encoding position sensing system,
for example, the Acu-Rite-II manufactured by Bausch and Lomb Company of
Rochester, N.Y., which comprises a fixed ruler or scale 64 attached to
table 38 and an eye or sensor 66 attached to member 52 of trolley 48 for
determining the position along ruler 64 at which trolley 48 is located.
The digital output from optical sensor 66 is provided to sample position
controller 30 of FIG. 1 so that sample position controller 30 can compare
this with the desired position indicated by the digital signal from system
controller 22 and provide appropriate control signals to motor 62 for
rotation of screw 60 to accurately position trolley 48. Table 38 can also
be provided with limit switches 68 which provide appropriate control
signals to sample position controller 30 which limits the length of travel
of trolley 48 from hitting stops 69 on table 38.
Tube 56 is centered in the X-ray field 70 of CAT 34. The attachment of tube
56 to members 54 of trolley 48 and 50 by a screw or other suitable
fastening means causes trolley 50 to move when trolley 48 is moved by
means of screw 60 and motor 62. Tube 56 which preferably is made of
material that is optically transparent and mechanically strong and has a
low X-ray absorption, for example, plexiglas, has a removable window 72 to
facilitate the positioning of sample holder 74 in tube 56. A core sample
75 is positioned in sample holder 74 as indicated by dotted lines. The
ends of sample holder 74 are positioned in central apertures of discs 76,
which can be made of a low friction material, for example, nylon, and are
sized such that they make a close sliding fit to ensure centering of the
sample inside tube 56. Discs 76 are locked in position in tube 56 by
screws 78 which can be made of, for example, nylon. In addition, discs 76
can be provided with a plurality of apertures 80 sized to accommodate
fluid lines and electrical power lines from various equipment associated
with sample holder 74.
Sample holder 74 can be a pressure-preserving, core-sample container used
in normal coring operations; however, if standard X-ray energy associated
with CAT scan analytic equipment, such as the Deltascan-100 mentioned
hereinabove, the pressure vessel must be made of material that will allow
the X-rays to pass through the container walls, for example aluminum,
beryllium or alumina. Aluminum is preferred because it absorbs a portion
of the low energy spectra, thus making the beam more monochromatic.
Nevertheless, steel pressure containers can be employed if higher energy
X-ray tubes or radioactive sources are used. Alternatively, sample holder
74 can be replaced by any unpressurized or unsealed container which is
suitable for holding a core sample or other material in a fixed position.
In the case of a frozen core sample the container can be positioned inside
an insulating cylinder which can be made of, for example, styrofoam or
other thermally insulating materials with low X-ray absorption. This
insulating cylinder can be filled with dry ice or the like to keep the
core sample frozen. If it is desired to heat a core sample, a heating
element which has a low X-ray absorption, such as the heating foil
manufactured by Minco Products, Inc. of Minneapolis, Minn., can be wrapped
around the container to heat the sample and a similar insulating cylinder
can be used.
In an alternative embodiment, tube 56 can be replaced by an elongated
member, such as an I-beam, which is suitably attached to trolleys 48 and
50. In this embodiment sample holder 74 can be suitably secured to the
elongated member, or other suitable means, for example, an enclosure
suitably sized for holding the sample can be securely fastened to the
elongated member. It should be noted that throughout the discussion of the
preferred embodiment reference has been made to a core sample from a
borehole; however, this reference is merely exemplary and is not intended
as a limitation of the utilization of the sample positioning system of the
present invention. Rather, any material can be placed in a suitable sample
holder which is attached to or is an integral part of the member which
couples trolleys 48 and 50. In addition, other guide means can be used in
place of rails 44, for example, grooves in the upper surface of tables 38
and 40. Still further, motor 62 and screw 60 can be replaced with any
means for horizontal movement.
As discussed hereinabove, tables 38 and 40 have legs 42 which are suitably
attached to, for example, the floor, to ensure that tables 38 and 40
maintain proper alignment with CAT 34. This alignment is originally
obtained by mounting optical cross hairs in the center of each side of the
aperture of X-ray field 70 and mounting identical cross hairs in the
center of each member 54. An optical transit is set up and legs 42 are
adjusted so that all cross hairs are on line when trollies 48 and 50 are
at either end of tables 38 and 40. When proper alignment is obtained legs
42 are locked in place.
It is to be understood that variations and modifications of the present
invention can be made without departing from the scope of the invention.
It is also to be understood that the scope of the invention is not to be
interpreted as limited to the specific embodiments disclosed herein, but
only in accordance with the appended claims when read in light of the
foregoing disclosure.
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