U.S. patent number 3,878,395 [Application Number 05/423,665] was granted by the patent office on 1975-04-15 for method and means for operating x-ray tubes with rotary anodes.
This patent grant is currently assigned to Siemens Aktiengesellschaft. Invention is credited to Gunther Appelt, Gerd Seifert.
United States Patent |
3,878,395 |
Seifert , et al. |
April 15, 1975 |
METHOD AND MEANS FOR OPERATING X-RAY TUBES WITH ROTARY ANODES
Abstract
In X-ray tubes anodes are used which, are maintained in rotation
during the production of X-rays for fluoroscopy and which anodes
are supported by friction-diminishing members. The anodes are
maintained in rotation for all operational periods during which
there may be a wish to take X-ray radiographs. The anode is
supported magnetically without contact, except an electrical one
for transmitting current to the anode.
Inventors: |
Seifert; Gerd (Erlangen,
DT), Appelt; Gunther (Erlangen, DT) |
Assignee: |
Siemens Aktiengesellschaft
(Munich, DT)
|
Family
ID: |
5865127 |
Appl.
No.: |
05/423,665 |
Filed: |
December 11, 1973 |
Foreign Application Priority Data
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|
|
|
Dec 21, 1972 [DT] |
|
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2262757 |
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Current U.S.
Class: |
378/132;
378/93 |
Current CPC
Class: |
F16C
32/0402 (20130101); H01J 35/103 (20130101) |
Current International
Class: |
H01J
35/10 (20060101); H01J 35/00 (20060101); G03b
041/16 () |
Field of
Search: |
;250/402,520,406
;313/60 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Lawrence; James W.
Assistant Examiner: Church; C. E.
Attorney, Agent or Firm: Richards & Geier
Claims
What is claimed is:
1. A process for operating rotary anodes of X-ray tubes, comprising
magnetically supporting the anode free from contact except for a
support transmitting the X-ray current and rotating the anode
continuously during the entire period in which there is a
possibility that an X-ray photograph will be taken.
2. The process in accordance with claim 1 wherein the magnetic
support is radial and the current transmitting support is
vertical.
3. A rotary anode X-ray tube provided with a mechanical bearing
means for giving mechanical support to the rotary anode when it is
rotating in its operative disposition and serving to conduct tube
current passing by way of the anode, and magnetic bearing means
adapted to give additional support to the anode magnetically when
it is so rotating thereby enabling the anode to remain in the said
operative disposition, while rotating, without further mechanical
support, said magnetic bearing means being arranged to give the
anode radial support relative to its rotary axis, and said
mechanical bearing means being arranged to give the anode axial
support.
4. An X-ray tube as claimed in claim 3 wherein said mechanical
bearing is adapted to give the anode vertical support.
5. An X-ray tube as claimed in claim 3 wherein the said magnetic
bearing means comprises a first stack of aligned annular
electromagnet coils which extend, longitudinally of the rotary axis
of the anode, along and within a second stack of such coils, said
first stack being located radially inwards of a rotary part of the
anode that is surrounded by the said second stack in an internal
space bounded by the said rotary part, alternate coils in each of
the stacks being adapted to produce mutually opposed magnetic
fields when energized in a predetermined manner, and the said
rotary part having magnetically conductive portions arranged to
extend, with clearance, between said first and second stacks so
that magnetic forces exerted on the said rotary parts by the stacks
when the coils thereof are energized hold the anode in its
operative disposition when rotating.
6. An X-ray tube as claimed in claim 5 wherein the said rotary part
is a hollow cylindrical part arranged concentrically about the
rotary axis of the anode.
7. An X-ray tube as claimed in claim 5 wherein the said
magnetically conductive portions comprise a plurality of annular
members which extend around the said rotary axis and are aligned
longitudinally thereof.
8. An X-ray tube as claimed in claim 5 wherein the said first and
second stacks are arranged concentrically around the said rotary
axis.
9. An X-ray tube as claimed in claim 5 wherein the said
magnetically conductive portions are arranged so as to rotate, when
the anode is rotating in its operative disposition, freely past
respective further magnetically conductive portions that are
mounted radially inwards of the said rotary part and serve as
magnetic yokes for the said first stack.
10. An X-ray tube as claimed in claim 9 wherein the said further
magnetically conductive portions comprise a plurality of annular
members which extend along the said rotary axis and are aligned
longitudinally thereof.
11. An X-ray tube as claimed in claim 5 wherein the said
magnetically conductive portions of the said rotary part are
arranged so as to rotate, when the anode is rotating in its
operative disposition, freely past respective further magnetically
conductive portions that are mounted radially outwards of the said
rotary part and serve as magnetic yokes for the said second
stack.
12. An X-ray tube as claimed in claim 5 wherein the anode has
arranged axially between an anode plate thereof and that end of the
said stacks nearer to the anode plate a drive part with which a
stator winding extending freely around the drive part is adapted to
cooperate to cause rotation of the anode when the stator winding is
energized in a predetermined manner.
13. An X-ray tube as claimed in claim 5 wherein said stacks are
divided into two parts which are separated from one another,
axially of the anode, by a drive part thereof which is surrounded
by a stator winding which is adapted to cooperate with the drive
part so as to cause rotation of the anode when the stator winding
is energized in a predetermined manner.
14. Apparatus as claimed in claim 3 wherein said mechanical bearing
is arranged to support the anode axially at a point situated where
the rotary axis of the anode intersects an imaginary perpendicular
drawn from an annular target surface which the anode provides,
extending concentrically about the said rotary axis, for an
incident electron beam.
15. An X-ray tube as claimed in claim 3, said tube being provided
with sensing means arranged to detect eccentricity of rotation of
the said anode and provide an electrical signal which is a measure
of such eccentricity, and with energization control means arranged
to control the supply of energization current to the electromagnet
coils of the first and second stacks in dependence upon the said
electrical signal, thereby to counteract such eccentricity by
damping.
Description
This invention relates to method and means for operating X-ray
tubes with rotary anodes, the anode of which is maintained in
rotation during X-ray fluoroscopy and is supported by
friction-diminishing members.
In using X-ray tubes with rotary anodes it is disantvageous that
prior to starting the production of X-rays, one has to wait until
the anode is brought to rotation. This is a loss of time which
lasts as a rule, up to some seconds. For that reason, expensive
starting devices were provided to shorten the starting time period.
On the other hand, due to the wear of usual bearings, which is the
most serious limit of the lifetime of rotary X-ray tubes, it is not
possible to let the anode turn continuously longer than is
necessary for specific radiographing situations. This is
particularly the case when it is desired to increase the load of
the anode possible during an extremely quick turning of the anode.
For such arrangements, additionally braking devices have been
provided in order, on the one hand, to diminish the bearing wear
which increases with the square of the rotary speed, and, on the
other hand, to diminish disturbing sounds which increase with the
rotary speed.
The present invention is based on the consideration that when X-ray
tubes with rotary anodes are operated, it is desirable to make
spontaneous photographs without having to take into consideration
disturbing or detrimental factors, such as, for example, the
starting time, noises and wear of the bearings.
Consequently, an object of the present invention is the provision
of a method by the use of which, within the usual operational
conditions, it is possible to have X-ray photographing devices with
rotary anodes which are ready for photographing at any time, while
providing sufficient stability for the tube.
A process of the present invention for operating X-ray tubes with
rotary anodes and accomplishing this object of the present
invention consists in that the anode is caused to rotate and
continues in rotation when and so long as there is a possibility of
an X-ray photograph being taken and that the anode is magnetically
supported without contact, with the exception of a preferably axial
bearing transmitting the tube current.
The present invention provides a rotary anode that can run for long
working periods, namely, for an entire working day or even longer,
without the bearing wearing out. Besides elimination of noises, the
tube is held in continuous working readiness for photographing.
Photographs can also be made at unpredetermined moments, which can
be of great importance for diagnosis. It is no longer necessary to
wait for the end of the starting time of the anode. Furthermore, it
is necessary to apply the starting energy to the anode only once
during a working period, and it is no longer necessary to apply
brakes to very quickly running anodes to avoid wear and noises. In
addition, it is possible to make the anodes run faster, so that the
speed of rotation can be adapted to the load without having to
consider the wear of the bearing. Due to magnetic support, there is
no contact of moving parts with the immovable parts, with the
exception of one connection through which flows the current of the
X-ray tube, such as an axial bearing.
Magnetic bearings are known in the art and are described, for
example, in the publication "Philips Technische Rundschau,"
1960/61, No. 7, pages 252 to 259. In these bearings, there is used,
as the force centering the axle, a repelling force between radially
magnetized ring-shaped inner magnets fixed to the axle and
ring-shaped outer magnets magnetized radially in the same manner
and fixed to the casing. The axial bearing also takes place by a
force acting between rings extending along the axle and similarly
magnetized. This construction has the drawback, as far as X-ray
tubes are concerned, that the ring-shaped inner magnets, namely,
those of the rotor, must be free from conduits; i.e., they must be
permanent magnets. However, the use of permanent magnets produces
all the drawbacks which permanent magnets have in comparison with
electromagnets. They age, they lose their residual magnetism at the
Curie point, and their residual magnetism even prior to the Curie
point is dependent on the temperature of at least up to 300.degree.
C reached in the bearings of the rotary anodes. Furthermore, in the
case of permanent magnets, the magnetization cannot be steered, at
least in the rotor. Permanently magnetized rings considerably
increase the actual weight of the rotor and thus the cost required
for its bearing.
On the other hand, electromagnets are difficult to insert into a
rotor since they require conduits. A feeding current must be
supplied through slides. This again produces friction and wear
which must be avoided. This is also one of the difficulties for
insertion of a motor into the vacuum space of the tube. One can
imagine that magnetic spools built into the rotor could receive
current from induction spools also fixed to the rotor. However,
field forces resulting from such an energy transmission would act
upon the rotor, and this is not desired, since the forces must be
taken from the magnetic bearing and they would increase
requirements made upon the magnetic bearing.
According to an advantageous construction of the present invention,
use is made of the above-described principle, and a structure is
used which permits the use of electromagnets without requiring
contact of rotary and fixed parts, such as slide contacts. A
bearing then consists of two coaxially arranged tubular piles
consisting of superposed electromagnetic rings which are
alternately opposedly magnetized. One of the piles, consisting of
so-called inner magnets, has a small diameter, and is located
within the other pile having so-called outer magnets with a large
diameter. Direct current flows through ring-shaped field windings
of all inner and outer magnets to produce a magnetic field.
Alternate opposed direction of magnetizing, which was already
accepted as necessary in the above-mentioned publication, results,
in that the ring spools are wound in opposite directions. To
provide magnetic poles which are precise in space, magnetically
conducting lugs directed toward each other are coordinated with the
magnetic rings, whereby lugs pertaining to magnets located within
the rotor are outwardly located lugs or yokes, while those
pertaining to the outer magnets are inwardly directed yokes. The
rotor is located without contact in the cylindrical space between
the piles of the inner and outer magnets. The rotor consists
largely of a non-magnetic material as, for example, copper.
According to one construction of the yoke arrangement, soft
magnetic rings are located upon its inner side. They are yokes of
inner magnets consisting of the same material, but without touching
them. The radial width of the overlapping is such that the poles of
the inner magnets extend outwardly, even if there is some
excentricity of the rotor relatively to the ring-shaped magnets,
over the soft magnetic rings, i.e., yokes, of the rotor. Then, the
ring-shaped outer magnets can exert repelling forces upon the rotor
without it being necessary to apply magnets to the rotor itself.
For this reason, electromagnets can also be used without it being
necesary to have slide contacts.
The distance between the inner edges of the yokes of the outer
magnets and the outer edges of the yoke rings of the rotor, which
can be indicated by the letter c, should be small so that the force
(which is opposed to the eccentricity of the rotor) has the highest
possible value, and the axial height of a magnetic ring should be
above three times greater than the distance c, according to
statements of best results indicated in the above-stated
publication.
When the rotor can receive high voltage relative to the outer
magnets, the distance c is fixed by the tension strength of this
stretch and is comparatively large (10 to 12 mm.) However, it can
also be small, and is determined solely by manufacturing tolerances
and the wall strength of the vacuum piston when the outer magnets
follow the rotor in their potential.
The yoke rings carried by the rotor overlap the inner magnets
without touching them. This overlapping can be provided by
segmenting the yoke rings provided in the rotor. Thus, the rotor
consists advantageously in the section pertaining to the magnetic
bearing out of a non-magnetic outer cylinder and a non-magnetic
inner cylinder which is rotationally safely fixed with tight fit in
the outer cylinder and which carries yoke rings of the rotor fixed
in grooves, possibly soldered. In order to facilitate mounting, the
inner cylinder and the yoke rings fixed thereon are cut into two
halves in a plane extending through the rotor axis. Thus, the inner
cylinder with the yoke rings separates into two equal segments as
soon as it is removed from the outer cylinder. These segments can
then be placed about the inner magnets and then held together by
positioning the outer cylinder. The axially directed attracting
forces which each inner magnet exerts upon two yoke rings of the
rotor are balanced by themselves due to the arrangement of the
rotor yoke rings in pairs in the rotor, provided that the two air
gaps between the inner magnet and the two corresponding yoke rings
of the rotor are equal in size. If the rotor is shifted axially
relative to the inner magnets, even if only to a small extent, then
one air gap becomes smaller to the extent of this shifting, and the
other one becomes larger to the same extent and the axially
operating forces no longer balance themselves in the rotor. Thus,
such a premeditated shifting of the rotor can produce a difference
in force and if so, the axle of the rotor can always be held in
contact with the axial bearing which, at the end of this axle, can
have the shape of a needle bearing or a supporting ball, and which
constitutes the contact required for the transmission of the anode
current. It is advantageous to place the axial bearing at such a
distance from the plate of the rotary anode that the axis of the
rotary anode intersects the imaginary vertical line upon the focal
point surface in the axial bearing. In that case, excentric or top
motions of the rotary anode do not produce any focal pivot
movements in the first approximation.
In the above-described arrangement, wherein outer magnets act
repellently upon yokes of the rotor magnetized by inner magnets and
thus upon the rotor, a return movement of the rotor into its
central position is provided in that the repellent force is
greatest precisely at the locations of the circumference of the
rotor yokes which are closest to the outer magnets due to the
eccentricity.
The operation of outer and inner magnets makes possible a damping
in the return movement in that high return forces are operative
only until a sufficient differential decrease of eccentricity with
the time - de/dt is reached, so that the rotor will not carry any
regulating swingings or only small ones about its central
location.
The operation of the magnets is thus dependent upon a signal which
is directly connected with the eccentricity of the moment. This
signal can be produced by placing two metal cylinders coaxially
about the rotor without touching the outer magnets, and the
capacity between these two cylinders acts more or less out of time
upon a swinging circuit and thus upon the oscillation amplitude of
this swinging circuit. The capacity between these two cylinders is
then dependent upon the eccentricity, since the electrical fields
are formed from one of the two cylinders to the other cylinder
substantially over the rotor. Finally, the oscillation amplitude of
the resonance circuit can actuate currents in the field windings of
the magnets through an electronic regulating stretch, the
characteristic of which is adapted to the top motion conditions of
the rotor.
The invention will appear more clearly from the following detailed
description when taken in connection with the accompanying
drawings, showing, by way of example only, preferred embodiments of
the inventive idea.
In the drawings:
FIG. 1 is a sectional side view of an X-ray tube with rotary anode,
suitable for the purposes of the present invention.
FIG. 2 is a transverse section along the line II-- II of FIG.
1.
FIGS. 3 and 4 are sections through two different constructions of
magnetic bearings.
FIG. 1 shows a vacuum container 1 having at one end the cathode
arrangement 2 and at the other end the anode combination 3. In this
case, the actual glow cathode 4 is fixed by a support 5 in an
innerly directed tube 6 of the glass container 1. A support 8 is
melted into the side of the vacuum container 1 located opposite the
tube 6. The bearing 8 carries ring-shaped field windings of
electromagnets indicated by numerals 9 to 15. The field windings 9
to 15 are amplified into ring-shaped inner magnets by the yokes 16
to 23 of soft magnetic material as well as the soft magnetic
support 8. Furthermore, a plate disc 7 is placed vacuum-tightly in
the support 8 by a more or less strong tensioning. This plate holds
a point bearing 24, which is slightly shiftable in axial direction.
The anode combination 3 is held in axial direction in electrical
contact with the member 7 through the point of the carrying spindle
24 located in the bearing 24. The rotor 27 is provided at the upper
part of the axle 25, constructed as a spindle close to the anode
plate 26. As already stated, the rotor consists of two non-magnetic
hollow cylinders stuck one within the other, and carries upon its
inner side yokes 28 to 35 of soft magnetic iron. These yokes are
magnetically in engagement with yokes 16 to 23 of electromagnets
with the field windings 9 to 15. Thus, the yokes 28 to 35 extend
further outwardly the fields of the windings 9 to 15. In the
illustrated example, the fields of the windings 36 to 42, as
located at the outer side of the tube container 1, are arranged
precisely in space above the yoke rings 43 to 50 fixed upon the
soft magnetic cylinder 71. These fields repel the yoke rings 28 to
35, and thus act repellently upon the rotor. A stator 52 is
arranged in the known manner on the outer side of the container 1
at the rotor end distanced from the rotary anode plate 26 and the
actual driving part 51 of the rotor 27. A potential cylinder 72 is
provided to keep small the space between the yokes 43 to 50 and the
vacuum container 1 without causing improperly high electrical field
strength at the inner edges of the yokes 43 to 50 (due to high
voltage which the anode 3 provides during X-ray photographing
relative to ground, thus also relative to outer magnets located at
the ground potential).
The functioning of the present invention in the illustrated example
takes place in that a current is switched on which is received from
the source through conduits 73, 74 and 75 into the switch device 55
and through the conduits 56 and 57, and the insulation stretch with
secondary rectification 76 is directly transmitted to field
windings 9 to 15 and through conduits 77 and 78 to the field
windings 36 to 42. Thus, a support of the rotary parts of the anode
3 in the radial direction is produced without contact. This is
based on the repelling forces of the magnetic fields emanating from
the windings 36 to 42 and acting upon yokes 28 to 35 magnetized by
field windings 9 to 15. The capacity between the probe 60 and the
potential cylinder 72 is measured from the device 55 through
conduits 58 and 59. This capacity is a measure for the immediate
eccentricity of the anode combination 3 relatively to the two
magnetic ring devices. The device 55 also contains means operating
the currents in the conduits 56 and 57, resp. 77 and 78, depending
upon the extent of eccentricity and the extent of change of
eccentricity in time. The eccentricity or the change of
eccentricity in time causes the device 55 to transmit such currents
through the conduits 56 and 57 and the conduits 77 and 78 and thus
through the field windings of magnets within and outside of the
rotor, that forces are exerted upon the rotor which are opposed to
eccentricity, but which act against the eccentricity only to the
extent that the rotor will not carry out regulating swingings about
its central position.
X-rays are produced in the known manner, on the one hand, by
supplying current necessary for sending electrons through the
conduits 61 and 62 of the glow cathode 4, and on the other hand, by
applying high voltage 65 of a few 10.sup.5 v. produced by the
generator 64 located at the net 73, 74 and 75 between the glow
cathode 4 and the conduit 63, which is in galvanic contact with the
rotary anode 26. Thus, the electrons emitted by the glow cathode
are transmitted by the stator 52 relative to the alternating
current of the generator 64 or two-phase alternating current 66
over conduits 67, 68, and 69; they are accelerated by the rotating
anode 26, and their kinetic energy is transformed there in a known
manner into X-rays which leave the tube as a cone-shaped bundle
70.
FIG. 2 shows the arrangement of the field windings 13 and 40 as
well as those of the interengaging yokes 20 and 32 and of the yoke
47 located in one plane in the yoke 32. The wall of the vacuum
container 1 is visible between the yoke 32 and the yoke 47. The
outer yoke rings 43 to 50 are fixed to the magnetically soft
cylinder 71, and the inner yoke rings 16 to 23 are fixed to the
soft-magnetic support 8. The spindle 25 moves in the center of the
hollow support 8.
FIG. 3 shows the driving part 51' of the rotor 27' and the stator
52' arranged upon the end of the staple of magnets directed to the
rotary anode plate 26'. Thus, the distance of the staples 79 and 80
from the rotary anode plate 26' is greater than the distance of the
rotary anode plate from the magnetic staples according to the
construction of FIG. 1. This is of particular advantage when the
rotary anode is to be very heavily loaded. Due to the increased
space, the passage of heat is also longer, and the magnetic staple
79 as well as the staple will be subjected only to low
temperatures. Furthermore, in this construction, the inner staple
79 acts repellently upon the yokes 81 and 82, located at the rotor
27'. The yokes 84, 84 and 85 belong to the outer staple 86, which,
due to the necessarily smaller air gap between the yokes of the
rotor and those of the outer magnets, must lie upon the anode
potential. The yokes 83, 84 and 85 extend through the wall 86 of
the container 1 of the tube. This construction has the advantage
that there is an intensive force action of the magnetic field from
the staple 79 to the yokes 81 and 82 due to the small gap 87,
while, in the construction of FIG. 1, in addition to the gap, the
wall of tube container 1 is also located between the magnets and
the yokes.
In the construction shown in FIG. 4, the driving member 51" and the
stator 52" are arranged in the middle of the length of the carrying
spindle 25". Due to this arrangement, the two magnetic staples are
divided into two parts; namely, two separate supports are produced.
Thus, for inner magnets are produced partial staples 88 and 89,
which are held at a distance from each other by a distancing holder
90 corresponding to the length of the driving member 51". The outer
magnet is also divided into staples 91 and 92, which are
counterparts of the staple parts 88 and 89. In this construction, a
mechanical separation is provided between the inner staples 88 and
89 and their coordinated rotor yokes 93, 94 and 95, 96, and also
between staples 91 and 92 and their yokes 83' to 85', 97 and 98.
The space 87' is the same as the space 87 of FIG. 3. Only the wall
99 of the container 1" consists of glass and is not penetrated by
the yokes 83' to 85', 97 and 98, but on the inner side of the wall
94, there is a holding coating 100 which holds the yokes 83' to
85', 97 and 98. This construction, in addition to deviating from
the constructive structure of the yokes and the magnetic staples,
has the advantage that the magnetic supports can have the greatest
possible distance from each other in the manner usual for ball
bearings at a predetermined length of the axle 25". In this
construction, a stable support is produced while accepting heating
in staple 88 greater than in construction of FIG. 3.
The length of the axle 25 (FIG. 1) is so selected that the
imaginary vertical line 101 upon the focal point path 102 of the
anode 26 cuts in the contact point of the axial bearing 24. This
can be the supporting point of the pointed end of the axle 25
constructed as a spindle. A similar axial support is provided by a
ball 104 (FIG. 4) located between the end of the axle 25" having a
flat or concave shape and the counter bearing 105, namely, the
inner wall of the connecting member 106.
* * * * *