U.S. patent number 3,878,394 [Application Number 05/377,741] was granted by the patent office on 1975-04-15 for portable x-ray device.
Invention is credited to John P. Golden.
United States Patent |
3,878,394 |
Golden |
April 15, 1975 |
Portable X-ray device
Abstract
A portable X-ray source device for producing a selected number
of uniform X-ray output pulses. The device comprises a spiral
capacitor voltage generator, a transformer assembly and a
cold-cathode emitter X-ray tube. The capacitor and transformer are
coaxially disposed in mating sections of a cylindrical canister
which is evacuated and filled with oil. The tube is disposed
centrally within the capacitor and transformer for packaging
efficiency. Corona suppression means are provided for preventing
high voltage damage within the canister. The X-ray tube employs an
emitter comprising spaced rings of woven graphite material. A spark
gap trigger device including tungsten electrode strips is mounted
on the outside of the canister where it can occupy the corner space
of a square sheet metal housing. A slide-in battery cartridge and
high power converter circuit are provided for dc operation.
Inventors: |
Golden; John P. (Ann Arbor,
MI) |
Family
ID: |
23490336 |
Appl.
No.: |
05/377,741 |
Filed: |
July 9, 1973 |
Current U.S.
Class: |
378/102; 378/103;
378/121 |
Current CPC
Class: |
H01F
30/10 (20130101); H01J 35/165 (20130101); H05G
1/20 (20130101); H05G 1/24 (20130101); H01F
27/40 (20130101); H01J 35/22 (20130101); H03K
3/537 (20130101); H01F 2027/408 (20130101) |
Current International
Class: |
H01F
27/00 (20060101); H01F 30/10 (20060101); H01F
30/06 (20060101); H01J 35/22 (20060101); H01J
35/00 (20060101); H01J 35/16 (20060101); H03K
3/537 (20060101); H05G 1/24 (20060101); H03K
3/00 (20060101); H01F 27/40 (20060101); H05G
1/20 (20060101); H05G 1/00 (20060101); H01j
035/00 () |
Field of
Search: |
;250/401,402,417,418,421 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Lawrence; James W.
Assistant Examiner: Anderson; B. C.
Attorney, Agent or Firm: Young; Thomas N.
Claims
The embodiments of the invention in which an exclusive property or
privilege is claimed are defined as follows:
1. An X-ray source device comprising: a voltage generator including
a wrapped foil spiral capacitor of cylindrical configuration; a
transformer unit including cylindrical windings; the capacitor and
transformer unit being coaxially disposed in axially spaced
relation; a sealed cylindrical metallic canister containing both
the capacitor and transformer unit and being electrically connected
to each; an X-ray tube disposed coaxially with the capacitor and
transformer unit, and trigger means electrically connecting the
tube to said capacitor to received voltage pulses therefrom.
2. Apparatus as defined in claim 1 wherein said canister comprises
first and second axially aligned cylindrical portions.
3. Apparatus as defined in claim 2 wherein said first and second
portions are threaded for complemental joining thereof.
4. Apparatus as defined in claim 1 further comprising spark gap
trigger means electrically connected to said capacitor for
discharging same at a predetermined voltage level, said trigger
means being externally mounted on the sidewall of said
canister.
5. Apparatus as defined in claim 4 including a housing for said
canister and X-ray tube, said housing having a substantially
rectangular configuration in cross section.
6. Apparatus as defined in claim 4 wherein said spark gap trigger
means comprises first and second spaced electrodes, the first
electrode being electrically isolated from said canister and
electrically connected to the high voltage foil of said capacitor,
said second electrode being electrically connected to the low
voltage foil of said capacitor through said canister.
7. Apparatus as defined in claim 1 wherein said capacitor comprises
a cylindrical support member of conductive metal having radially
flared ends and carrying said wrapped foil capacitor concentrically
thereon, and a pair of annular metallic end plates secured to and
in electrical contact with said support member.
8. Apparatus as defined in claim 7 including a dielectric corona
shield cantilevered to an end plate of said support member.
9. Apparatus as defined in claim 1 wherein said transformer unit
includes at least one primary winding and one secondary winding,
and a rectifier bridge electrically connected across the secondary
winding, the components of said bridge being disposed on and
carried by said transformer unit between said spaced cores.
10. Apparatus as defined in claim 1 wherein said transformer unit
includes at least one primary and one secondary winding, a dc
voltage source, and a power converter circuit connected between
said source and said primary winding to convert an ac input voltage
to dc.
11. An X-ray source device comprising a housing, a spiral capacitor
within said housing, a transformer electrically connected to the
capacitor and having at least a primary winding and a secondary
winding of cylindrical configuration and disposed within said
housing coaxial with but axially spaced from said capacitor, a
spark gap trigger device in said housing, an X-ray emitting tube,
means electrically connecting said capacitor secondary winding and
trigger device to said tube to provide high voltage pulses thereto,
a battery cartridge including a dc source, a cartridge receptacle
within said housing and accessible to an outer surface thereof,
means for permitting said cartridge to be slidably inserted into
and removed from said receptacle, means including connector means
for connecting said source to said primary winding when the
cartridge is in the receptacle, said connector means including a
first portion fixed to said cartridge, said first and second
portions being aligned with the axis of sliding displacement of
said cartridge relative to said housing for electrical engagement
and disengagement as said cartridge is slided into and out of said
receptacle.
12. Apparatus as defined in claim 11 including a door normally
covering said receptacle but having open and closed positions, said
door being pivotally connected to said housing for movement between
said positions, said open position being wholly within said
housing, and means for biasing the door to the closed position.
Description
INTRODUCTION
This invention relates to X-ray source devices and particularly to
a pulsed-output X-ray device of improved design and operation. The
invention further relates to improvements in certain components for
X-ray source devices including transformers, triggering devices,
and X-ray tubes.
BACKGROUND OF THE INVENTION
The X-ray source device to which the present invention relates is
of a relatively small and often portable variety and is to be
distinguished in terms of size, power output and pulsed rather than
continuous wave output from the large radiology equipment typically
used in hospitals for diagnostic examination of the human body. The
X-ray source device to which the present invention relates is
typically and particularly usable in connection with veterinarian
diagnosis, concealed package examination, bomb and weapon detection
systems in airports, and in any other application where a small,
transportable and easily operated device is required. It may, of
course, be used for examination of humans as well.
Prior art X-ray source devices of the relatively small and
transportable type typically comprise an X-ray tube of the cold
cathode type, a high voltage generator in the form of a spiral
capacitor and a trigger device which, when actuated, applies a
short duration pulse of electrical energy from the generator to the
X-ray tube. Some prior art devices include means for selecting the
number of output pulses to be generated during a given examination
process, the number of pulses selected typically being a function
of the depth and difficulty of X-ray penetration in the device
being examined. A fully portable device typically comprises all of
the above-named components arranged in a relatively small package
having suitable protection against radiation and high voltage
leakage and, in addition, a power supply including a battery and a
dc to ac converter to energize the high voltage generator.
As will be understood by those familiar with the X-ray art, the
X-ray source devices are usable with various types of image
gathering apparatus including simple photographic plates,
fluoroscopes, etc.
The small, transportable X-ray devices of the prior art present a
certain number of deficiencies particularly with respect to the
uniformity of the X-ray output; i.e., the pulses of electromagnetic
energy are neither uniform in power level nor in distribution or
pattern. In addition, the prior art devices exhibit short tube
life, low efficiency, cumbersome packaging and a tendency toward
internal destruction from high voltage leakage and corona effects.
Thus, there exists a need for a substantially improved X-ray source
device of the small transportable type so as to eliminate the
numerous significant problems of the prior art.
BRIEF STATEMENT OF THE INVENTION
The subject invention is an X-ray source device of the relatively
small transportable type providing a pulsed output and exhibiting
improved efficiency, substantially improved uniformity of X-ray
power level and distribution pattern, long component life and
convenient and efficient packaging. In general, the features and
advantages of the present invention are provided by the improved
design of the overall X-ray source device, the improved design and
construction of a number of individual components of the X-ray
source device and the integration of those components into a
convenient and readily usable package.
In accordance with the first more specific aspect of the present
invention, a transformer of improved design and location is
employed for the production of a high output voltage pulse sequence
of selectable number. The transformer of the subject invention
comprises a plurality of windings disposed on a dielectric bobbin
or winding form, and the disposition of a relatively large number
of "external," laminated steel cores around the windings of the
transformer, said cores being disposed so as to enclose or surround
the transformer windings at their specific locations. Further, the
plurality of cores are circumferentially spaced around the windings
so as to form a transformer package having a hollow center through
which other components in the X-ray source device may extend. In
the specific embodiment hereinafter described in detail, the cores
are silicon oriented steel cores of the "C" design, such "C"
sections being joined together end-for-end in pairs and bound
together with plated steel bands. In addition, the transformer
design of the illustrative embodiment facilitates the mounting of
all output stage components including, for example, diode
rectifiers, directly on the periphery of the transformer windings
and between the circumferentially spaced cores thereof so as to
form an integrated and unitary output unit including both primary
and secondary transformer windings and other electrical components
associated therewith.
As suggested above, a further feature of the invention is the
location of the transformer output unit within a housing, said
location being coaxial with and forward of the capacitive voltage
generator, the center axis of the two devices defining an elongated
space which accommodates the X-ray tube.
In accordance with a second specific feature of the invention, a
high voltage generator is provided in the form of a spiral
capacitor. The capacitor comprises a combination of two copper foil
plates which are separated from one another by suitable dielectric
material, such as Mylar and paper, and wrapped in a spiral fashion
on a suitable form so as to be connectable to the transformer for
the application of high voltage pulses to the X-ray source tube. In
accordance with the present invention, the spiral capacitor and the
aforementioned transformer are disposed together in a coaxially and
axially spaced fashion within a metallic canister which is
electrically maintained at ground potential and which comprises two
open cylindrical sections adapted to be joined by means of a
threaded connection whereby the disengagement of the two metal
sections results in the electrical disconnection of the spiral
capacitor from the transformer.
In accordance with a third specific feature of the invention, an
X-ray source tube of the cold cathode type is provided. The X-ray
source tube of the subject invention comprises, in the preferred
form, an elongated and sharp pointed tungsten anode mounted in an
evacuated glass envelope of the reentry type to avoid arcing
between the electrodes thereof, and a cathode emitter of annular
design. The emitter comprises one or more axially spaced annuli of
high resistance fabric-like material disposed adjacent, concentric
with, but spaced from the pointed end of the tungsten anode. In the
illustrative form of the invention hereinafter described in detail,
the cathode emitter comprises two annuli of graphite fabric
material held together in a press-fit, two-part cathode assembly
housing, the two annuli of graphite cloth material having central
apertures of varying diameter in conformity with the varying
diameter along the axis of the pointed anode thereby to provide
uniform spacing between the interior diameters of the several
emitter annuli and the anode surface.
The subject invention also comprises a method and apparatus for
forming the cathode assembly as described above, said apparatus
comprising a two-part, press-fit cathode assembly housing, a punch,
and a Teflon block or equivalent for use during the punching
operation. In the illustrative embodiment described hereinafter,
the cathode assembly comprises a first housing portion of generally
cylindrical configuration having a flange of enlarged diameter so
as to define an internal step and a retainer ring which is
press-fit into the first portion to sandwich one or more graphite
cloth wafers which have been precut to the internal diameter of the
stepped portion of the cathode housing. A Teflon or equivalent
backup block is then placed against one side of the now
peripherally secured graphite cloth wafers and a punch having a
circular blade is driven through the cathode housing and the
graphite cloth wafer to remove an interior circular area of
predetermined diameter.
A still further feature of the present invention involves the
design and location of an improved spark gap trigger device for
automatic generation of the voltage pulses by discharge of the
spiral capacitor when a predetermined charge level is reached.
Whereas in the prior art devices the spark gap trigger device is
typically located remotely from the spiral capacitor and connector
therewith by way of leads, the spark gap trigger device of the
present invention is disposed on the external surface of the
aforementioned metal canister which holds the spiral capacitor and
transformer assembly. In the preferred embodiment hereinafter
described, an opening is cut or otherwise formed in the cartridge
at a point which is external of the spiral capacitor, and one foil
plate of the capacitor is connected to a tungsten electrode on the
interior of the spark gap trigger device. The opposite tungsten
electrode is secured through a bracket and cap assembly to the
canister and is, thus, at ground potential. To provide packaging
efficiency, the spark gap trigger device is mounted on the external
surface of the cylindrical cartridge and the cartridge is located
within a square or rectangular housing in such a fashion as to
place the trigger device in an otherwise vacant corner volume of
the housing. The trigger device of the present invention is
completely self-triggering and, thus, responds solely to a
predetermined voltage or charge having been attained in the
capacitor and does not require the use of active semiconductor
devices, such as SCR's and transistors.
The present invention comprises a number of still further features
and advantages, which together with those briefly described above,
give rise to a vastly-improved product having vastly-improved
performance and long life. These features and advantages will be
hereinafter described in specific detail but for the present,
suffice it to say that such advantages include but are not limited
to the mounting of the spiral capacitor within the metal container
in such a fashion as to eliminate corona discharge possibilities
and the resulting destruction of interior components, the
cantilevered relationship between a dielectric voltage shield and
the cylindrical form on which the spiral capacitor is wound, a
novel packaging concept involving a unique housing and handle
design, a slideout battery cartridge including terminals in the
cartridge and a spring-loaded door which is automatically closed
upon removal of the battery cartridge, and the inclusion of a
variable pulse initiation delay feature so as to permit the
operator to physically remove himself from the unit before the
X-ray pulses are generated.
These and other advantages of the present invention will be best
understood from a reading of the following description of the
specific embodiment of the invention, this specification to be
taken with the accompanying drawings hereinafter briefly
described.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side view, with parts broken away, of a portable X-ray
source device embodying the various features and advantages of the
present invention;
FIG. 2 is a side view, in full section, of the internal components
and the metallic canister of the device of FIG. 1;
FIG. 3 is an end view, partially sectioned, of the apparatus of
FIG. 2 showing the details of the spark gap trigger device and the
location thereof on the canister;
FIG. 4 is a plan view of the trigger device base electrode
assembly;
FIG. 5 is a perspective assembly drawing of the transformer and
output unit of the device of FIGS. 1 and 2;
FIG. 6 is a side view in cross section of the X-ray tube cathode
assembly;
FIG. 7 is an electrical system block diagram for the device of
FIGS. 1 and 2; and,
FIG. 8 is a schematic diagram of an illustrative input stage for
the device of FIGS. 1, 2, and 5.
DETAILED DESCRIPTION OF THE SPECIFIC EMBODIMENT
FIG. 1
Referring to FIG. 1, the invention is shown to be embodied in a
small, low power, pulsed output portable X-ray source device 10
comprising a metallic housing 12 having a substantially square or
rectangular cross section and preferably being fabricated out of
sheet aluminum or the like. Housing 12 is fitted on the right-hand
end thereof as seen in FIG. 1 with a shallow hood 14 within which
is disposed an X-ray tube housing cap 16 through which the X-rays
are directed during operation of the device. The housing 12 has
formed in the left-hand end thereof a receptacle 18 within which is
slidably disposed a battery cartridge 20 such that the X-ray source
device 10 may be operated on dc power in a portable mode. The
housing 12 is provided with a sturdy carrying handle 22 which is
suitably secured to the housing and which, in the illustrative
embodiment, carries a number of the electronics components which
are involved in the timing and control of the X-ray output
pulses.
Looking more specifically to the interior details of the handle 22
as revealed in the broken-away portion of the view of FIG. 1, the
longitudinal portion of the handle is hollowed out to receive a
pair of elongated circuit boards 24 and 26 which carry the timer
and pulse counter electronics components, including resistors,
capacitors, transistors, and the like. In addition, the handle
carries on the interior thereof a semiconcealed start switch 28
having an interior terminal portion 29 which is wired to the
circuit boards 24 and 26 by conductor means, not shown. The handle
22 further carries an exposure control device 30 including two
thumbwheel switches and a suitable digital indicator for selecting
the number of pulses to be generated between one and ninety-nine in
accordance with the depth and difficulty of penetration of the
device or article to be examined. Again, the pulse counter control
is a prior art device and will not be described in great detail,
other than to say it is suitably interconnected with the
electronics components on the circuit boards 24 and 26.
Additionally, handle 22 carries a delay selector 32 having an
interior terminal portion 33 and which may be actuated by the
operator to select a delay period up to 1 minute between the
depression of switch 28 and the X-ray pulse generation so as to
enable the operator to remove himself from the X-ray area when such
precautions appear to be advisable due to the nature of the device
being X-rayed. More specifically, it is well known that some
explosive devices may be contrived in such a fashion as to be
detonated by X-ray examination and, accordingly, for the safety of
the individuals performing the examination, the delay 32 permits
these individuals to retire to a safe distance before the output
pulses are generated. Finally, a safety lamp 34 is provided in the
top of the handle 22 to indicate that power to the device has been
turned on.
In the interior of the housing 12 there is disposed a cylindrical
canister 36 hereinafter described in greater detail with reference
to FIG. 2. The canister 36 contains the principal electronic parts
of the X-ray source device including the high-voltage generator,
the high-voltage transformer, and the X-ray tube as hereinafter
described. The canister 36 terminates at the right-hand end thereof
in the tube housing cap 16 and is suitably secured within the
housing 12 by such support means as will be readily apparent to
those skilled in the art.
An electrical connector 38 is disposed on the innermost end of the
battery cartridge 20 and is adapted to make contact with a
low-voltage transformer connector 39 which interconnects the dc
power from the battery cartridge 20 to the timer and counter
electronic circuit boards 24 and 26 through the terminal device 40
and to the high-voltage transformer within the canister 36 through
the low-voltage transformer 41 and other circuitry hereinafter
described.
As also shown in FIG. 1, housing 12 is provided at the left-hand
end thereof as shown in FIG. 1 with a mode select switch 42 which
operates to select either ac or dc power operation for the device
10. As also shown on the lower left-hand end of FIG. 1, a door 43
is pivotally disposed within the battery cartridge receptacle 18
and is spring biased to pivot around point 45 to a closed condition
whenever the cartridge 20 is slidably removed from the receptacle
18. Conversely, when the cartridge 20 is slidably disposed in the
receptacle 18, the door 43 simply pivots into the position shown in
FIG. 1 where it is out of the way of the cartridge 20.
Finally, the housing 12 is provided with feet 47, made of a
resilient material such as high-density rubber, so that the device
10 may be conveniently be placed on a support surface, such as a
table top, without damage either to the housing 12 or to the
support surface.
FIG. 2
Looking now to FIG. 2, the internal details of the canister 36 and
the interior components of the X-ray source assembly will be
described in detail. As shown in FIG. 2, the canister 36 comprises
hollow, cylindrical sections 44 and 46 of which section 46 is
provided with a threaded interior collar 48 to engage an internally
threaded portion of the section 44 so that the two sections 44 and
46 may be screwed together and apart as desired. An O-ring seal 49
is disposed between the two sections 44 and 46, such that the
entire interior of the canister 36 may be evacuated and filled with
oil and sealed.
As hereinafter described in detail, joining the canister sections
44 and 46 serves to make an electrical connection between a
high-voltage, transformer output unit 50 and a spiral capacitor 52
which operates as the high-voltage generator. Both the output unit
50 and the spiral capacitor 52 are disposed within the sealed
canister 36, the output unit 50 being within the cylindrical
section 46, and the spiral capacitor 52 being within the
cylindrical section 44. To make the high voltage connection between
units 50 and 52, the output unit 50 carries an annular high-voltage
contact 51 which engages a ring 53 on the spiral capacitor 52 when
the canister sections 44 and 46 are fully screwed together. The
ring 53 is electrically connected to the high-voltage plate of the
capacitor 52 for charging the same.
Discussing the assembly of FIG. 2 in greater detail, the output
unit 50 and spiral capacitor 52 are disposed within canister 36 in
coaxial, but axial spaced relationship, and are both of such a
configuration as to provide a continuous, hollow interior volume
within which is disposed an elongated cylindrical X-ray tube 54
having a reentry-type glass envelope 55. Tube 54 receives at the
left-hand end thereof a high-voltage contact 56 which is disposed
through a corona suppresser member 57 and connected to the high
voltage plate of the spiral capacitor 52.
On the right-hand side of the assembly of FIG. 2 the canister
section 46 is shown terminating in an annular end plate 58 which is
threadedly engaged with the tube housing cap 16, as shown. In
addition, an O-ring seal 59 is disposed between the threadedly
engaged portions of the canister section 46 and the end plate 58 to
maintain the oil seal, previously described. At the left-hand end,
the canister 36 is provided with an external retainer ring 60 which
threadedly engages the canister portion 36 and a rear cover plate
62 which, together with a high-voltage cantilever support member
64, holds in place a resilient diaphragm 66 to accommodate
expansion and contraction of the oil within the canister 36 with
varying temperature conditions. The significance of this last point
involves the fact that it is essential to evacuate the interior of
the canister 36 before use, such that no air bubbles remain trapped
in the oil, since the presence of such air bubbles could contribute
to corona discharge and eventual destruction of the interior
components of the device. The diaphragm 66, thus, operates in the
manner of a bellows to accommodate the varying volume of the oil in
the presence of temperature changes.
The spiral capacitor 52 comprises a metallic mounting cylinder 68
upon which is disposed a plurality of circumferentially spaced
inner ferrite strips 70 and a plastic or other dielectric
cylindrical form 72 upon which are wound in parallel, interleaved
fashion two mutually insulated copper foil strips separated from
one another by layers of Mylar and paper. In the specific
embodiment shown in FIG. 2, the copper foil strips are each
approximately 21/2 inches in width by 30 feet in length and are
wrapped up upon one another to form a pair of spaced parallel
capacitor plates having a large number of turns. Connection between
the high voltage foil of capacitor 52 and the contact 56 for tube
54 is made by bringing the foil through a slot in plastic coil form
72 and running a conductive copper strip between form 72 and
ferrite strip 70 to the aluminum ring 80. This ring is in contact
with cylinder 68 and an end plate 86, both of which are conductive.
By having cylinder 68 at the same voltage as the capacitor foil,
corona discharge in this area is suppressed. A second plurality of
spaced ferrite strips 74 are disposed around the outside of the
capacitor 52 and a retaining cylinder 76 of plastic or other
suitable dielectric material is disposed therearound to maintain
the ferrite in place. The ferrite strips 70 and 74 substantially
increase the output of a given spiral capacitor. A positioning ring
78 is disposed between an internal shoulder on the canister section
44 and the capacitor 52 assembly, as shown, to maintain the
assembly in the proper axial position within the canister 36.
For corona suppression, a metallic corona shield ring 80 having the
radially flared configuration illustrated in FIG. 2 is disposed
around the interior of the capacitor 52 on the right-hand end
thereof, as shown in FIG. 2, and, as previously mentioned, is
maintained at a high voltage by connection to the capacitor foil.
The suppressor ring 80 abuts the ferrite strips 70 on the internal
diameter of the capacitor plate winding arrangement and bears
against a cylindrical lead shield 82 which lies between the
capacitor 52 and the X-ray tube 54. The lead shield 82 extends the
full length of the tube 54, as shown, and terminates at the
left-hand end adjacent an annular shield portion 84, as shown. The
corona suppression apparatus further comprises the metallic end
plate 86 disposed on the left-hand side of the capacitor 52, as
shown in FIG. 2, and having the flared configuration shown. The
corona suppresser plate 86 is threadedly engaged with the
cantilevered high-voltage support ring 64, as shown.
Looking now to the interior of the X-ray tube 54, the high-voltage
contact 56 in corona suppressor 86 engages a high-voltage contact
rod 88 which is disposed within a plastic tube housing 90 so as to
make contact with the left-hand end of a tungsten anode 92 by way
of a contact plunger 94 and a contact spring 96 within the reentry
portion of the X-ray tube envelope 55. The anode 92 is an elongated
and pointed structure, as shown, and cooperates with a cathode
assembly 98 hereinafter described in greater detail with reference
to FIG. 6 to produce X-ray output pulses upon the application of a
high-voltage pulse sequence to the anode by way of the contact 56.
These X-ray pulses are directed through the lead collimator washer
100 and the fiberglass window 102 to the object under examination
by way of the tube housing cap 16.
The tube housing 90 is threadedly engaged at the right-hand end
with a retainer collar 104 which in turn is fixed to the end ring
58 so as to engage the cylindrical lead transformer shield 106
which is disposed within the interior volume of the transformer
output unit 50. A lead shield ring 108 of cylindrical configuration
is also disposed around the cylindrical path through which the
X-ray beam travels on route to the device being examined for
protection of the transformer unit 50. A plurality of feed-through
terminal plugs 107 are disposed in the end ring 58 to bring leads
from the transformer unit 50 to the external devices in the handle
22.
The details of the transformer unit 50 are partially apparent from
the cross sectional view of FIG. 2 and are also apparent from the
perspective view of FIG. 5 and the detailed description of the
transformer output unit 50 will be given under the FIG. 5 heading
found hereinafter.
FIGS. 3 AND 4
Looking now to FIGS. 3 and 4, the details of the spark gap trigger
device which operates to apply the high-voltage pulses from the
spiral capacitor 52 to the X-ray tube 54 will be described.
As shwon in FIG. 3, the canister 36 has the spark gap trigger
device 110 mounted on the external surface thereof and the canister
36 is positioned within the housing 12 of FIG. 1 such that the
spark gap trigger device occupies a corner volume which is
otherwise wasted space within the housing because of its
substantially square or rectangular cross-sectional configuration.
The spark gap trigger device comprises an oblong rectangular
bracket 112 of conductive metal, such as aluminum, a top plate 114
which is disposed on the oblong bracket 112 and secured thereto by
fastener means, such as screws, an interior electrode support plate
116 which is maintained in position within an opening formed in the
wall of the canister 36 by an insulative material 118, such as
potting compound. The electrode plate 116 supports in the center
thereof an elongated strip-like tungsten electrode 120. High
voltage capacitor foil 122a is soldered to support plate 116 and
is, thus, connected to electrode 120. The low voltage foil 122b of
capacitor 52 is electrically connected to a contact rod 123 which
abuts the canister 36 and, thus, is electrically connected to
electrode 124 by way of bracket 112 and cover plate 114. The
tungsten electrode 124 which is carried by cover plate 114 is
parallel, but radially spaced in relationship with the electrode
120. Accordingly, the electrodes 120 and 124 are electrically
insulated from one another by the air gap therebetween, this gap
being such as to break down and provide a spark discharge
thereacross whenever the voltage difference on the capacitor foil
exceeds a predetermined magnitude. Note that a slot is provided in
the cylinder 76 through which to bring the foils to the trigger
device 110.
FIG. 5
Looking now to FIG. 5 and also to FIG. 2, the details of the
transformer output unit 50 will be described. This unit comprises
fine and heavy transformer windings 126 and 127, respectively,
disposed on a dielectric winding form 128 and surrounded by ten
external cores 130. Each of the cores 130 comprises two C-shaped
silicon-oriented steel core sections, each comprising a plurality
of laminations to eliminate internally circulating currents. Each
of the C-shaped core sections is secured together by means of a
plated steel band 132 so as to form a closed core structure, thus,
leaving the center of the transformer output unit 50 hollow to
accommodate the X-ray tube 54. A plastic washer 133 is disposed
between the cores 130 and the left-hand end of the canister section
46, as shown in FIG. 2 to hold the contact 51 previously described.
The coil form 128 is preferably bounded at the right and left-hand
ends thereof as seen in FIG. 2 by conductive connectors 134 and
136, respectively, so as to accommodate the electrical
interconnection of a plurality of circuit components 138a through
138d between the transformer windings as hereinafter described in
greater detail with reference to FIG. 8 and in such a way as to
permit the components 138 to be positioned circumferentially
between the cores 130. Accordingly, the transformer output unit 50
may be substantially prewired and premanufactured for disposition
within the canister section 46 in the fashion of a module.
Moreover, this construction contributes to the overall efficiency
with which space is utilized in the device 10.
FIG. 6
Looking now to FIG. 6, the details of the cathode assembly 98 which
forms part of the X-ray tube 54 will be described. In addition, a
method for manufacturing the cathode assembly 98 of FIG. 6 will
also be described.
As shown in FIG. 6, the pointed tungsten electrode 92 has a tapered
portion 140 about which are spaced woven graphite fabric cathode
rings 142 and 144. Rings 142 and 144 are held in place by means of
an internally stepped cathode support tube 146 having a radial
interior shoulder, a press fit spacer or separator 148 and a
cathode clamp ring 150 which is also press fit within the tube 146.
A nickel window 152 is held in place adjacent the right-hand end of
the assembly 98 between the cathode clamp ring 150 and the end ring
154. It will be noted that the woven graphite fabric cathode rings
142 and 144 are provided with interior diameters which vary as
between the two rings so as to maintain a substantially uniform
spacing between the outer surface of the tapered portion 140 of the
anode 92 and the interior diameters of the cathode rings.
The cathode assembly 98 is preferably manufactured by first cutting
out a pair of wafers of graphite fabric, these two wafers having
equal diameters as suggested in FIG. 6. The wafer which makes up
ring 142 is first placed within the cathode assembly tube 146 and
the separator 148 is press fit into place. A tool having an
external diameter mating with the interior diameter of tube 146 and
carrying a circular cutting blade on the end thereof is then driven
through the tube. The blade passes through the wafer held between
separator 148 and tube 146 to remove the circular center thereof.
The wafer is preferably backed up by a block of Teflon or
equivalent plastic to prevent tearing the delicate material
thereof. The second wafer and the ring 150 are then put in place
and a second tool with a smaller diameter circular blade is driven
through the tube 146 to remove the center of graphite ring 144.
Again a back up block is employed. The larger diameter hole of ring
142 is unaffected by the second cutting operation. Additional rings
may be formed by a straightforward extension of this process,
additional separators being required, of course.
The formation of the rings 142 and 144 within the assembly 98
reduces the amount of handling of the delicate graphite cloth and
ensures a relatively precise shape and interior diameter thereof.
This is of extreme importance inasmuch as the life of the X-ray
tube is primarily a function of the durability of the cathode
structure. In prior art devices where a plurality of needle-like
structures are used in place of the more uniform and homogeneous
graphite rings 142 and 144, it has been found that an extremely
nonuniform discharge pattern occurs between the anode 92 and the
various cathode needles, thus, causing some of the needles to be
eroded away quite rapidly, such that the tube effectively wears out
in a relatively short time. Moreover, the X-ray pattern which
emerges from such a prior art tube is extremely nonuniform.
Finally, the power level of the X-ray output tends to vary in the
prior art devices from one pulse to the next whereas the uniform
cathode ring arrangement shown in FIG. 6 tends to produce an
extremely uniform output pattern and pulse level.
FIG. 7
Looking first to FIG. 7, a block diagram of the electrical
arrangement of the components within the device 10 is shown. As
shown in the block diagram, the circuit comprises a power control
unit 200 which is essentially disposed within the handle 22 of FIG.
1 and which receives a first input from the switch 42, as shown,
and a second input from the switch 28, as shown. When both switches
are turned on, the power control unit 200 operates to provide
either dc power from the battery cartridge 20 or ac power from an
inverter assembly 202 to the high voltage transformer output unit
50. The power control unit 200 operates with or without a delay in
accordance with the setting of the delay timer 32. The high-voltage
transformer output unit 50 then provides a charging voltage to the
high-voltage plate of the spiral capacitor 52 which is connected
electrically in parallel with the electrodes 120 and 124 of the
spark gap trigger device 110 and the anode and cathode of the X-ray
tube 54. Whenever the voltage reaches the predetermined level, a
discharge or arcing occurs between the electrodes 120 and 124,
thus, to apply a high-voltage pulse to the X-ray tube 54. It will
be noted that the cathode of the X-ray tube 54, the electrode 124,
and one of the plates of the capacitor 52 are all connected to the
system ground 204. A feedback signal is derived from the junction
between resistors 206 and 208 and is fed by way of line 210 to the
counter assembly 212. The counter is essentially a pulse counter
and is set by the thumbwheel switches which form part of the unit
30 shown in FIG. 1.
Accordingly, one may set the unit or device 10 for any number of
output X-ray pulses from one to ninety-nine, may further set a
delay time of up to one minute or more by means of the delay timer
32 and thereafter depresses the hand switch 28 so as to cause a
high voltage to be applied to the spiral capacitor 52. Once the
capacitor 52 is charged up to a predetermined level, the arcing or
discharge between the electrodes of the trigger device 110 occurs
and applies a transient to the tube 54 to produce the X-ray output
pulses. When the predetermined number of pulses has been generated,
the feedback signal on line 210 applied to the counter assembly 212
causes a "stop" signal to be applied to the power control 200 by
way of line 214, thus, terminating any further application of the
high-voltage signal to the spiral capacitor 52. The counter 212 is
reset via line 215 each time the switch 28 is depressed.
FIG. 8
Looking now to the circuit of FIG. 8, the electrical details of the
inverter assembly 202 as well as the nature of the windings 126 and
127 in the transformer output unit and the interrelation thereof
with the feedback line trigger device and spiral capacitor are
shown.
In FIG. 8, mode select switches 42, 42', and 42" are all capable of
being positioned in each of the ac and dc positions so as to permit
the device 10 to operate off of the battery cartridge 20 or
directly from an ac power source through terminal block 301. When
operated in the dc mode, the 28.8 volt output of battery cartridge
20 is connected to a first inverter stage 300 through resistors 334
and 336. The inverter stage 300 is a conventional push-pull
converter comprising PNP-type transistors 302 and 304 having the
collector electrodes thereof connected to opposite ends of a
center-tapped primary winding 306. Voltage stability is provided by
means of a Zener diode 308 having one electrode connected commonly
to the emitters of transistors 302 and 304 and the other electrode
connected through diodes 310 and 312 to the opposite ends of the
transformer winding 306. The push-pull operation of the inverter
stage 300 is provided by means of the inductive cross coupling
which results from the center-tapped winding 307 the opposite ends
of which are connected to the base or control electrodes of
transistors 302 and 304.
Primary winding 306 drives secondary windings 314 and 316 which
form part of a second inverter stage 318 comprising transistors 320
and 322. The second stage 318 is similar to the first stage 300 and
further comprises a precision Zener diode 326 and current-limiting
diodes 328 and 330. The transistors 320 and 322 have the emitter
electrodes thereof connected through the switches 42' and 42",
respectively, to opposite ends of the center-tapped primary winding
324. It will be noted that the center tap of primary winding 324 is
returned to the 28.8 volt battery cartridge 20 by way of the hand
switch 28 as well as the mode select switch 42. Winding 324 drives
secondary winding 330 to provide the high-voltage signal which is
applied through a diode inverter bridge 332 to the capacitor 52 and
also to the electrodes 120 and 124 of the spark gap trigger device
110. The voltage divider resistors 206 and 208 which provide the
feedback signal to the counter by way of line 210 are also shown in
FIG. 8.
When the circuit of FIG. 8 is operated in the ac mode, switches 42,
42', and 42" are all set to the ac positions, thus, to apply ac
power through the hand switch 28 directly to only the upper half of
the primary winding 324. The ac signal is also applied via line 340
to the auxiliary winding 338 which effectively takes the place of
the lower half of the primary winding 324 in the ac mode.
The windings 306, 307, 314, 316, 324, and 330 are all part of the
windings represented by reference character 127 in the detailed
cross-sectional view of FIG. 2. Winding 330 in FIG. 8 corresponds
to winding 126 in FIG. 2. Moreover, the diode bridge components 332
as well as various other components in the inverter circuit of FIG.
8 may be disposed in the positions represented by the position of
components 138 of FIG. 5.
In a practical embodiment of the invention, the circuit of FIG. 8
is capable of producing a rectified output of approximately 7
kilovolts thereby to charge the spiral capacitor 52. The
transistors in the second stage 318 of the circuit of FIG. 8 are
preferably high-power transistors capable of conducting 15 amperes
or more. The primary winding 338 preferably comprises 250 turns of
No. 27 wire, the upper and lower halves of the primary winding 24
comprise 65 turns each of No. 27 wire and the secondary winding 330
comprises 26,000 turns of No. 40 wire.
Additional detailed information regarding the theory of operation
of a high-votlage high-voltage capacitor may be found in the
Proceedings of the IEE, Volume 111, No. 4, April 1964, pages 849
through 855, "Novel Principal of Transient High Voltage
Generation," by Fitch and Howell.
It is to be understood that the invention has been described with
reference to a specific embodiment thereof and various
modifications, changes, additions, and rearrangements are possible
within the scope of the art and, accordingly, the foregoing
description is not to be construed in a limiting sense.
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