U.S. patent number 3,714,427 [Application Number 05/056,581] was granted by the patent office on 1973-01-30 for apparatus for taking section radiographs.
This patent grant is currently assigned to U.S. Philips Corporation. Invention is credited to Jurgen Lemmrich, Friedrich Reiniger, Reinhard VON Hacht.
United States Patent |
3,714,427 |
Reiniger , et al. |
January 30, 1973 |
APPARATUS FOR TAKING SECTION RADIOGRAPHS
Abstract
An apparatus for taking section radiographs with the x-ray tube
being movable in two mutually perpendicular directions
simultaneously by two separate electric motors. The speeds of the
motors are independently variable so that the tube's movement can
describe any desired path including an ellipse, while the x-ray
source is also adjustable.
Inventors: |
Reiniger; Friedrich (2
Hamburg-Sasel, DT), VON Hacht; Reinhard (2083
Halstenbek, DT), Lemmrich; Jurgen (2 Hamburg 57,
DT) |
Assignee: |
U.S. Philips Corporation (New
York, NY)
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Family
ID: |
5740377 |
Appl.
No.: |
05/056,581 |
Filed: |
July 20, 1970 |
Foreign Application Priority Data
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Jul 19, 1969 [DT] |
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P 19 36 915.4 |
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Current U.S.
Class: |
378/25; 378/197;
378/91 |
Current CPC
Class: |
H02P
27/026 (20130101); A61B 6/4464 (20130101); A61B
6/541 (20130101); A61B 6/548 (20130101) |
Current International
Class: |
A61B
6/02 (20060101); A61B 6/00 (20060101); H02P
27/02 (20060101); G01n 021/00 (); H01j
037/00 () |
Field of
Search: |
;250/61.5,93,91,92
;318/575,576,577 |
Foreign Patent Documents
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1,118,397 |
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Nov 1961 |
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DT |
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1,138,617 |
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Oct 1962 |
|
DT |
|
Primary Examiner: Lindquist; William F.
Claims
What is claimed is:
1. In an apparatus including an X-ray source and using an X-ray
film cassette for taking section radiographs, the improvement in
combination therewith comprising drive means including an electric
motor for moving the X-ray source along a predetermined path which
includes a central position, and for simultaneously moving the film
cassette along said path in the opposite direction, circuit means
for controlling said motor including means for sensing the position
of the X-ray source along the path relative to said central
position and for providing sequential time signals, a plurality of
motor-current thyristor pairs connected in parallel opposition and
having gate terminals receiving said time signals from said means
for sensing, whereby the X-ray source is returned to its central
position after each cyclical movement along said path.
2. An apparatus as claimed in claim 15 characterized in that said
drive means comprises means for sensing load fluctuations and for
adjusting the speed of said drive means corresponding to said
change in load.
3. An apparatus for taking section radiographs as claimed in claim
2 characterized in that said drive means comprises an induction
motor, and said circuit means varies the speed of the motor by the
variation of the effective supply voltage.
4. An apparatus as claimed in claim 3 characterized in that said
circuit means provide a voltage proportional to the speed with a
polarity depending upon the direction of rotation, which voltage is
compared with a determined voltage, the difference in value acting
upon a phase angle control, which shifts the instants of ignition
of thyristors included in the conductors of the motors so that the
difference in value is minimized.
5. An apparatus as claimed in claim 4 characterized in that at the
zero passage of the value difference the field of rotation is
reversed.
6. An apparatus as claimed in claim 4 characterized in that the
determined voltages for the drives in both directions are varied in
accordance with a program which provides a displacement of the
X-ray source along one path within the rectangle determined by the
maximum paths of displacement.
7. An apparatus as claimed in claim 6 characterized in that
patterns representing the desired speed variations of the swinging
paths are provided, which are scanned in accordance with the
desired-speed variation for displacing potentiometer tappings from
which the determined voltages for the control-circuits of the
drives for the longitudinal and transverse directions are
derived.
8. An apparatus as claimed in claim 6 characterized in that the
determined voltages are produced by a function generator, the
desired curves being formed by a substantially straight line,
sinusoidal and parabolic arcs.
9. An apparatus as claimed in claim 4 characterized in that the
determined voltages for the drives in the two directions vary
sinusoidally in time, a phase shift of one quarter period occurring
between the zero passages of the determined voltages.
10. An apparatus as claimed in claim 1 wherein said X-ray tube is
displaced, prior to the exposure, along said path out of the
central position, which path is tangential to a predetermined
swinging path at a main peak point, from where it terminates in the
swinging path.
11. An apparatus as claimed in claim 10 characterized in that the
speed of the X-ray source at the instant of reaching said main peak
point corresponds to the speed along the swinging path.
12. An apparatus as claimed in claim 10 characterized in that the
X-ray source is switched on when it has reached said main peak
point.
13. An apparatus as claimed in claim 10 characterized in that it
comprises a determined voltage generator which varies the
determined voltages in accordance with a program which causes the
X-ray source to run smoothly from the central position to the
swinging path, from where it returns to the central position at the
termination of the exposure.
Description
The invention has for its object to provide an apparatus for taking
section radiographs comprising an X-ray tube adapted to be moved by
motive force along a predetermined path in two direction parallel
to each other.
Apparatus of this kind are known, comprising a driving motor
providing, via suitable mechanical means, a generally sinusoidal
displacement of the X-ray source in a longitudinal and a transverse
direction so that the X-ray source performs an elliptical or
circular swinging movement and apart from a layer focussed on a
blurred figure arises. With such apparatus the number of potential
swinging paths is restricted. Moreover, the transition from one
swinging path to another requires a change-over of the apparatus,
for example, by resetting stops which limit the displacement in the
longitudinal and/or the transverse directions. Therefore,
remote-control of a change-over from one path of movement to
another is not possible.
When the X-ray source is moved sinusoidally in time, the speed at
the center is at a maximum; therefore, in these apparatus the
swinging path must not start at the center, because the initial
speed is too high. Consequently, the swinging movement starts from
a lateral position of the X-ray source, in which the central beam
strikes the patient obliquely to the table top. If it is desired to
take graphs with this apparatus with a perpendicular central beam,
for example, Bucky graphs, first the driving mechanism for the
section radiographs has to be disengaged and the tube has to be
moved into its central position.
The invention has for its object to obviate these disadvantages in
an apparatus for taking section radiographs of the kind set forth.
According to the invention this problem is solved in that the
movements of the X-ray source in the two directions are obtained by
two relatively independent motor drives, the speed of rotation of
which is variable during exposure.
The invention will be described more fully with reference to one
embodiment shown in the drawing.
FIG. 1 is an elevation of an apparatus for taking section
radiographs embodying the invention.
FIG. 2 is a block diagram of one of the motor drives and
FIG. 3 illustrates the course of the desired values and the speed
of rotation for an elliptical path of the X-ray source.
FIG. 1 shows the narrow side of a table top 1 of an apparatus for
taking section radiographs, on which the object 2 to be examined is
lying. The object 2 is exposed to an X-ray source 3, which is
adapted to be moved in the direction of the arrow 4 and at right
angles to the plane of the drawing, while the central beam of the
X-ray source is constantly orientated to the same point of the
object. The X-ray source is coupled with the film cassette 5
located beneath the table top 1 via a longitudinal rod (not shown)
so that the X-ray source and the film cassette 5 are moved in
relatively opposite senses.
The X-ray source 3 is held by a telescopic ceiling support 12,
which is secured to a carriage 6, which is adapted to travel by
means of rollers 7 transversely of the direction of the
longitudinal axis of the table along rails 8, which are secured to
a further carriage 9, which is adapted to travel by means of
rollers 11 along rails 10 secured to the ceiling and extending
parallel to the longitudinal axis of the table 1. The longitudinal
carriage 9 is provided with a motor 13, which drives a spindle 14
engaging a nut 15 secured to the transverse carriage 6. In this way
the transverse carriage 6 can be displaced by motive force to the
left or to the right in accordance with the direction of rotation
of the spindle 14. A further motor 16, rigidly secured to the
longitudinal carriage 9, engages in the same way via a spindle a
nut (not shown), which is secured to the ceiling so that the
longitudinal carriage can be displaced by motive force at right
angles to the plane of the drawing. The nuts can be loosened so
that, if desired, the X-ray source may be moved by hand.
In the case of a linear swinging movement, for example, in the
direction of length of the table, only the motor 16 is operative,
preferably with a constant speed, after the transverse carriage 6
has been moved into the central position. In the case of a circular
or elliptical swinging movement the two motors 13 and 16 are
controlled so that their speeds are sinusoidally varied in time so
that between the maxima of the speeds a phase shift of one quarter
period is obtained and the transverse carriage reaches its extreme
lateral position at the instant when the longitudinal carriage is
just in its central position, whereas the longitudinal carriage
reaches its extreme position, when the transverse carriage is in
its central position. When the paths of displacement in the two
directions have the same lengths, a circle is obtained. In the
other cases the swinging movement is elliptical.
FIG. 2 shows the circuit diagram of a three-phase induction motor
particularly suitable for these purposes. The three conductors of
the induction motor 20 are connected via thyristor pairs 21, 22 and
23, connected in parallel opposition, to the terminals R,S,T of the
alternating-current mains. The torque produced by the motor depends
mainly upon the effective value of the voltage across the motor
winding or from the relative durations of ignition of the
thyristors. In order to maintain the speed constant also in the
event of load fluctuations, a control-circuit is provided which is
governed by the control-magnitudes proportional to the speed and
which acts upon the instants of ignition of the thyristors 21, 22,
23 so that the speed is independent of load fluctuations.
For this purpose the motor shaft 24 is provided with a D.C. or A.C.
tacho-generator 25, which supplies a voltage proportional to the
speed, which voltage is smoothed in the block 26 or rectified and
smoothed respectively. In the event of an A.C. tacho-generator this
measuring voltage has furthermore to be repolarized in accordance
with the direction of rotation (for example, positive polarity for
righthand rotation, negative polarity for left-hand rotation). This
change of polarity may be carried out by means of a mechanical
sense detector coupled with the motor shaft. However, it may
alternatively be controlled by means of an electronic sense
detector which detects the phase sequence of the phase voltages of
a multiphase A.C. tacho-generator. The resultant actual value is
supplied as a current to an operation amplifier 27 and compared
with a current produced by a function generator 31 having a
determined value, corresponding to the desired speed, the amplitude
of which is programmed. The amplified difference of both values
controls on the one hand a voltage-ignition-time converter, or gate
triggering device for producing time sequential trigger signals,
and on the other hand the determined value initiates at a zero
passage the reversal by changing over the motor phases. This may
also be chieved mechanically by causing a Schmitt trigger 28 to
excite a change-over switching member at the zero passage of the
control difference, which member reverses the field of rotation of
the motor 20. Alternatively, the ignition pulses may be
electronically conducted to two additional valve pairs, which
exchange the connections of two motor phases to the mains
conductors.
The outputs of the voltage-ignition-time converter, or gate
triggering device for producing time sequential trigger signals,
30, or gate triggering device for producing time sequential trigger
signals, are connected to the cathodes and the gate electrodes of
the pairs of thyristors 21, 22, 23 and control the ignition time of
these semiconductor elements. From a given instant of each half
period of the voltage, which is propagated with an increasing
control-voltage, short ignition pulses (30 .mu.sec) of medium
frequency (about 2 kHz) are applied to the gate electrodes of the
pairs of thyristors. The increase or decrease of the driving torque
obtained by the variation of the ignition time provides a
stabilization of the speed obviating the disturbances. If the
desired value is changed with such a speed control, the speed is
varied accordingly.
For the production of electrical signals having determined values
in accordance with desired speed regulations a current generating
device 31 is provided, the functioning of which will be explained
furtheron.
The motors 13 and 16 of FIG. 1 are equipped with such
control-circuits. Within the maximum limits of displacement in the
longitudinal and transverse directions all swinging paths that can
be programmed electronically can be adjusted by remote-control. The
swinging paths are in particular Lissajou's figures, but also any
other curves, for example, spirals etc.
The desired values for the two motors may be derived i.e. from a
pulse sequence whose frequency is determined by the duration of
circulation and the desired curve. The curve may be formed by
substantially sinusoidal and parabolic arcs and straight lines so
that all time intervals can be derived by division from this pulse
frequency. All time sections, for example, also the period of time
for one cycle of the X-ray source correspond to the time interval
between two pulses or a multiple thereof. By using a common pulse
sequence (time raster) for the two driving directions a fixed
relationship between the desired values of the longitudinal and
transverse movements of the X-ray source is obtained.
In order to obtain a circular or elliptical path the desired values
are varied sinusoidally in time so that between the sinusoidal
desired values (guiding magnitudes) a phase shift of one quarter
period is ensured. When the maximum speeds in both cases are the
same, a circle is obtained, otherwise it is an ellipse. If the
amplitude of one of the guiding magnitudes is varied, the maximum
speed and hence the swinging path of the X-ray source is varied
accordingly. This variation may, if desired, be performed by
remote-control.
As stated above, it is often desired to take also Bucky radiographs
by means of an apparatus for taking section radiographs, the X-ray
source then being in a central position and the central beam
striking the table top perpendicularly. This is possible in the
apparatus embodying the invention without the need for further
means, as will be explained hereinafter with reference to FIG.
3.
FIG. 3 shows the path of the X-ray source for taking a radiograph
of a section with an elliptical swinging movement. The direction of
length of the table is designated by x and the transverse direction
by y. The Figure illustrates, in addition, the time variation of
the desired values or the speeds of the drives for the x(n.sub.x)-
and y-direction (n.sub.y) as well as the distance of the X-ray
source from the x- and the y-axes corresponding to the time
integral of the speed in the x- and y-directions respectively. The
speeds vary in accordance with the desired values produced by the
desired-value-generator in accordance with a programme causing the
X-ray source to move from the center smoothly into an elliptical
path, from which it moves back also smoothly into the central
position.
At the instant of switching on (t = 0), when the X-ray source is
located at the center (x = 0; y = 0), the motor 13 (FIG. 1) starts
running and displaces the X-ray source in the y-direction
downwardly (FIG. 3). Its speed n.sub.y increases linearly up to the
instant t = T/4, then decreases linearly with time and attains zero
value at the instant t = T/2. The drive for displacing the X-ray
source in the x-direction starts at the instant t = T/4 and
displaces the X-ray source to the right. Its speed increases
linearly up to the instant t = T/2 and then decreases linearly to
zero value up to the instant t = 3/4 T. At the instant t = T/2 the
sense of rotation of the y-motor drive is reversed, the speed
varying sinusoidally and attaining its maximum at the instant t =
3/4 T. When the cross-hatched surface beneath this sinusoidal wave
corresponds with the shaded surface above the triangular
oscillation, the X-ray source has reached at this instant the
co-ordinate y = 0, while with an appropriate value of the drive in
the x-direction it is at a distance x = 0 from the y-axis. It is
located at the instant t = 3/4 T at the peak of the elliptical path
(x = x, y = 0). At this instant the exposure is switched on (the
instant of switching on is fixed by a given pulse of the sequence,
which coincides with the zero passage of the speed n.sub.x),
n.sub.y varies from that instant cosinusoidally, whereas n.sub.x
varies sinusoidally so that after a full period of the cosine or
sine oscillation respectively the X-ray source has performed an
elliptical path around the center and is again at the peak. At this
instant the speed of the drive in the x-direction again passes
zero, which may be utilized as a criterion for the termination of
the exposure. After termination of exposure n.sub.y follows a
cosine law for a further quarter period, after which it changes
into a triangular oscillation as at the beginning; n.sub.x varies
triangularly after the exposure, the peak of the triangle having a
direction opposite that at the beginning. It is thus ensured that
the X-ray source approaches the center (x = 0; y = 0) with the
speed 0 so that it need not be braked abruptly at this point, which
might give rise to vibrations. Then the programme of the
desired-value generator is terminated.
The duration T of one cycle along an elliptical path may lie
between 1 and 5 seconds. Sinusoidal oscillations of such a low
frequency can hardly be produced by RC- or LC-sine wave generators,
because they have a long running-in time (for example, 50 sec),
while for switching on the movement of the apparatus the zero
passage has to correspond to a phase. Therefore, a function
generator 31 is used, which produces short square-wave pulses,
which are combined by flip-flops in the appropriate manner and
converted into square-wave oscillations, from which by integration
a triangular oscillations can be derived. By amplitude-dependent
deformation sinusoidal voltages can be derived from these
triangular oscillations. The guide magnitudes may alternatively be
obtained by means of two patterns, or memory carriers such as
optical or magnetic tape containing stored information or plates
with openings of which the form corresponds to a specific to a
specific program for speed variation in time, which represent the
desired variation in time of the speeds in the x- and y-directions
and which are scanned optically or mechanically with a constant
speed, a potentiometer tapping being displaced accordingly, from
which the desired value is derived. In this particularly simple way
not only elliptical swinging figures but also any other swinging
figure may be obtained, which are located in rectangles
predetermined by the maximum trajectories in the x- and
y-directions.
As stated above, the time integral of one quarter sine oscillation
has to be equal to the time integral of one half of a triangular
oscillation in order to ensure that the X-ray source is accurately
moved from the center to the main peak of the elliptical path and
regains the center after termination of the exposure. If these
conditions are not satisfied, the X-ray source is no longer
accurately at the center at the end of the exposure. The difference
may, indeed, be comparatively small, but each new exposure brings
about excursions in the same direction so that the X-ray source is
constantly shifted further away from the center. This drift may be
obviated by an additional control-device which guides the X-ray
source after each exposure accurately to the center. For each
direction such a control-device is provided, which may comprise
feelers secured to the longitudinal carriage and the transverse
carriage (FIG. 1), which feelers detect whether the X-ray source
is, at the end of the run, (t = 2,5T) exactly at the center or is
not, the motor drive being actuated, if necessary, with slow speed
in the appropriate direction until the X-ray source is accurately
at the center. This is indicated in FIG. 3 by a broken line for the
time variation of speed in the y-direction.
If only a linear swinging movement (in the direction of length of
the table) has to be carried out, the motor 13 (y-drive) is
switched off so that only the programme for the x-drive is
performed. The X-ray source is then switched on only for the part
of the negative half period of the desired value, during which the
X-ray source moves with substantially constant speed. This part is
indicated in FIG. 3 by T.sub.1.
* * * * *