US 3714427 A
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.
Description (OCR text may contain errors)
United States Patent [191 Reiniger et al.
1541 APPARATUS FOR TAKING SECTION RADIOGRAPHS  Inventors: Friedrich Relnlger, Hatnburg-Sasel; Reinhard von Hacht, Halstenbek; Jurgen Lemmrich, Hamburg, all of Germany  Filed: July 20, 1970  Appl. No.: 56,581
 Foreign Application Priority Data July 19,1969 Germany ..P 19 36 915.4
 11.8. CI ..250/6L5, 250/91  ln1.Cl. ..G01I121/00,H01j 37/00  Field of Search ...250/61.5. 93, 91, 92; 318/575, 318/576, 577
111 .3,7l4,427 1 Jan. 30, 1973 References Cited FOREIGN PATENTS OR APPLICATIONS 1,118,397 11/1961 Germany ..250/61.5 1,138,617 10/1962 Germany ..250/61.5
Primary Examiner-William F. Lindquist Attorney-Frank R. Trifari  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,
s Claims, 3 Drawing Figures Fig.1
INVENTORS FRIEDRICH REINIGER, BY REINHARD VON HACHT and JURGEN LMMR ICH PAIENIEDJAN30 ms 3.714.427
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IN VEN TORS FRIEDRICH REINIGER.
BY REINHARD VON HACHT and JURGEN LEMMRIWCH APPARATUS FOR TAKING SECTION RADIOGRAPHS 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, remotecontrol 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 l4 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 ofa 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 a'nd 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. tachogenerator. 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 achieved mechanically by causing a Schmitt trigger 28 to excite a changeover switching member at the zero passage of the con trol 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 psec) 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 electricalsignals 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 l3 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 Lissajous 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 I 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,)- and y-direction (n,,) as well as the distance of the X-ray source from the xand the y-axes corresponding to the time integral of the speed in the xand 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 (1: 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, 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 T14 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 #47. At the instant I 772 the sense of rotation of the ymotor drive is reversed, the speed varying sinusoidally and attaining its maximum at the instant t ifiT. 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 I %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,), n, varies from that instant cosinusoidally, whereas n, 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, follows a cosine law for a further quarter period, after which it changes into a triangular oscillation as at the beginning; n 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 (it 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 squarewave 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 xand 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 xand 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 2,5 T) 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 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.
cordance 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 posi tion at the termination of the exposure.