US3348051A - Power supply for an X-ray tube having a frequency responsive feedback means for a variable frequency converter - Google Patents

Description

3,348,051 ESPONSIVE Oct. 17, 1967 wE|GHART ET AL POWER SUPPLY- FOR AN X-RAY TUBE HAVING A FREQUENCY R FEEDBACK MEA NS-FOR A VARIABLE FREQUENCY CONVERTER Original Filed May 16, 1963 5 Sheets-Sheet 1 IL WI IL BY W HTTORNEYS. I

Oct. 17, 1967 F, EI HART ET Ag 3,348,051

POWER SUPPLY FOR AN X-RAY TUBE HAVING A FREQUENCY RESPONSIVE ABLE FREQUENCY CONVERTER FEEDBACK MEANS FOR A VARI Original Filed May 16, 1963 5 Sheets-Sheet 8 YFW HTIORNFYS.

Oct. 17, 1967 w RT ET AL 3,348,051

N X-RAYTUBE HAVING A FREQUENCY RESPONS-IVE NS FOR A VARIABLE FREQUENCY CONVERTER POWER SUPPLY FOR A FEEDBACK MEA Original Filed May 16, 1963 5 Sheets-Sheet 5 I l I I I I I I I I I 'T|||||l.I||I|.. I I I l I I l 35 28 5 th 1W QR .3 NE Q ENE w fi w IJ 1&0

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F. G. WEIGHART ET L N X-RAY TUBE HAVING A FR Oct. 17; 1967 3,348,051 EQUENCY RESPONSIVE NCY CONVERTER POWER SUPPLY FOR A FEEDBACK MEANS FOR A VARIABLE FREQUE 5 Sheets-Sheet 4 Original Filed May 16, 1963 INVENTORfi 5 F l l l lmli n I Oct. 17, 1967 F. G. WEIGHART ET L 3,348,051

QUENCY HESPONSI ABLE FREQUENCY CONVERTER POWER SUPPLY FOR AN X-RAY TUBE HAVING A FEE NS FOR A VARI 5 Sheets-Sheet 5 FEEDBACK MEA Original Filed May 16, 1963 l l L BY flmz /mqzW' IHHHHIIMIHHII'II HTIWRNEY'S United States Patent 3,348,051 7 POWER SUPPLY FOR AN X-RAY TUBE HAV- ING A FREQUENCY RESPONSIVE FEEDBACK MEANS FOR A VARIABLE FREQUEN CY CON- VERTER Frederick Gordon Weighart, Brookfield, and Ramon F.

Forlastro, Newton, Conn., assignors to Automat on Industries, Inc., El Segundo, Califi, a corporation of California Continuation of application Ser. No. 280,936, May 16, 1963. This application Nov. 22, 1965, Ser. No. 508,960 Claims. (Cl. 250103) This invention relates to an X-ray apparatus, and more particularly, to such an apparatus which is of the portable battery-operated type.

This application is a continuation of copending application X-ray apparatus, Sr. No. 280,936, filed May 16, 1963, now abandoned, in the'name -of Frederick Gordon Weighart and Ramon F. Forlastro and assigned of record to Automation Industries, Inc.

- The usuai X-ray apparatus, whether used for material inspection or for medical purposes, is large, heavy and cumbersome. Furthermore, even the so-called portablef units require a standard or fixed power source, such as a 60 cycle per second power line. In many applications, these factors-do not constitute drawbacks. However, under other circumstances it may be desirable for the apparatus to be both portable and able to operate in the absence of an external power supply. Examples of such requirements are readily found in the military services. Whether the proposed use for the X-rayequipment is material inspection or medical diagnosis, it may often be desirable for the apparatus to be relatively portable for field use, able to withstand mechanical shock,'and not to be reliant on-thepresence of an external electrical power supply.

Accordingly, it is the primary object of this invention to provide X-ray apparatus suitable for operation from a self-contained battery supply. Other objects are to provide such an apparatus which is completely self-contained, portable, reliable, and safe to both the operator and to a patient. The manner in which these objects are accomplished will be apparent from the following description, the appended claims, and the figures of the attached drawing, wherein: Y FIGURES 1, 2 and 3 illustrate-in schematic form various. portions of the circuit of one embodiment of this invention; 7 a

, FIGURE 4 illustrates the interrelationship between FIGURES 1, 2 and 3;

.FIGURE 5 is an elevational view, partially cut away, of a tube head usable in this invention;

FIGURE 6 is a cross sectional view taken substantially along the planes of line 66 of FIGURE 5;

FIGURE 7 is a leftend view of the apparatus of FIG URE 5; v V V 1 FIGURES is a cross-sectional view taken substantially along the plane of line 88 of FIGURE 5; and

FIGURE 9 is a cross sectional View taken substantially along the plane of line 9.9 of FIGURE 5. Referring to the drawings in more detail, the present invention is particularly adapted to be embodied in an battery charging circuit or to the X-ray apparatus. A double-pole single-throw switch 17 serves as the on-off switch from the charger to the battery.

The battery charger comprises a pair of identical transistors 18 and 20 having their bases referenced from ground by means of break-down diodes 22 and 24. Diodes 22 and 24 have suitable break-down values corresponding to the charging voltage requirements of the individual battery sections 10 and 12. In the illustrated embodiment the break-down diodes 22 and 24 are Zener diodes of 32 and 10 volt values respectively. Each of transistors 18 and 20 is energized through a solid state rectifying diode 26 and 28 from the secondary 30 of a battery charging transformer 32.

Transformer 32 has a dual winding primary 34 and 36 for energization from either a 110 or 220 volt source, depending upon the position of the double-pole, doublethrow selector switch 38. With switch 38 in the position illustrated, the primary windings of the transformer 32 are connected in parallel for energization from a 110 volt supply. A pilot lamp 40 indicates when the primary is energized and a single-pole switch 42 serves as a discone nect switch for the transformer primaries.

An X-ray tube requires at least three types of control: first, a filament current control to adjust the temperature of the cathode, thereby controlling electron emission and tube current; secondly, a high voltage control for regulating the voltage applied between'the'anode and cathode; and third, a timer for precisely controlling the length of time the high voltage is applied to the tube.

Filament current control The filament regulating circuit, seen in FIGURE 2, in-

Kv. control The anode-cathode AC. voltage required'for the operation of the X-ray tube is provided by the inverter circuit shown in FIGURE 1. The inverter is energized from X-ray unit that is completely self contained and capable of operating without being connected to an external power source. a i

' a The electrical circuitry of this X-ray unit may be roughly divided into a power circuit, illustrated in FIG- URES 1 and 2,arid a timer circuit and tube head circuit, illustrated in FIGURE 3. Primary power for the circuit of this invention is derived from a rechargeable battery '10, 12, such as a silver-cadmium battery. A trio of ganged switches 14, 15 and 16 connect the battery either to the a drive circuit and a rate generator. The rate generator comprises a unijunction transistor 57 connected to operate as a sawtooth oscillator. The frequency of oscillation is controlled by an adjustable rheostat 58 and the output wave is as illustrated at (a). This frequency is approximately 400 cycles per second. 7

The output sawtooth is differentiated by means of capacitors 60 and 62 to form synchronizing pulses (b) that are substantially coincident with the trailing edges of the sawtooth waves. The synchronizing pulses are applied to a multivibrator circuit comprising transistors 64 and 66. This circuit switches in response to the synchronizing pulses (b) and produces the square wave output shown at (c).

The output square wave (0) from the multivibrator is applied to the base of an NPN switching transistor 68 Which, in turn, supplies the base of a switching transis tor 70. By using two switching type transistors for amplification purposes, the square wave output'is reproduced. V

A third switching transistor 72 is also provided. However, it forms a portion of the timing circuit, and its operation will be described in more detail in connection with the timer. Accordingly, for the present, it will suflice to Patented Oct. 17, 1,967

.merely state that the collector-emitter circuit of this transistor 72 may be considered as being open, i.e. nonconductive as this is its normal condition during the time the X-ray tube is energized.

The square wave (e) from the transistor 70 is coupled across the nonconductive transistor 72 to transistor 73 where itis further amplified and applied to the primary winding 74 of a square wave transformer 76. The center tapped secondary 78 of transformer 76 provides balanced outputs180" out of the phase to the bases of inverted transistors 80 and 82 and to the center tapped primary Winding 84 of' the inverter output transformer 86.

The illustrated inverter is a standard parallel inverter circuit in which current flows alternately through transistors 80 and 82. The circuit also includes a pair of feedback diodes 83 for maintaining a square wave output (1).

The output (7) is applied to an inductive filter 88. The

output of filter 88 is a sine wave as shown at (g) and has a frequency corresponding to the fundemental of the square wave. The amplitude of the sine wave is inversely proportional to the reactance of the filter and, thus, the

' output frequency. The sine wave (g) is then applied via wave (f).

A transistor 100 has its base connected, to ground through a resistor 102 and to the rectified D.C. output.

from diode 96 through 'a breakdown diode 104 which, in one embodiment of the invention, is a 20-volt Zener diode; When diode 104 is not conducting, the base of.

The prior art makes use of a number of dilferent devices;

for timing X-ray exposures. Many of these require the switching of high current or high voltage. Also, relays or electro-mechanical timers have been employed, These are subject to mechanical failures and are relatively expensive. In the present circuit, accurate timing is achieved by low-power electronic means. 7

The timer control circuit of this invention is illustrated in FIGURE 3. The circuit includes a timer-actuating switch 110 which is arranged to connect a capacitor 112- to either the negative voltage supply of C through potentiometer 114 or directly to ground through contact 116 (switch 110 is illustrated in the normal 01f position).- The opposite side of capacitor 112 is connected to a diode 118 and from the diode ,to the base of transistor 122 and to ground through resistor 120. Under stabilized conditions with switch 110 positioned as illustrated, the capacitor 112 becomes charged to the polarities indicated and presents an open circuit to D.C. The diode is thus subjected to a voltage of proper polarity to cause a current flow in the base-emitter circuit of transistor 122. Ac cordingly, the collector-emitter circuit of the transistor 126 is open, as its base is grounded.

Still another switching transistor follows :transistor 126. This is the switching transistor 72 shown in'FIGURE 1, which has beenpreviously referred to. It will be noted that the base of this transistor is connected directly to the collector of transistor 126 and that its emitter is con nected in the common emitter fashion with transistors'122 the transistor 100 may beconsidered as grounded so that s the transistor presents an open circuit to the D.C. voltage. Under these conditions, the upper plate of the capacitor 99 becomes positive and establishes the control voltage which is supplied through conductor 106 to the output of the unijunction transistor 57.

When the feedback voltage of conductor 92 exceeds the breakdown voltage of Zener 104, the resulting current flow is applied to the base of transistor 100, causing this presents a closed circuit to ground, decreasing the control voltage by shunting a portion of it to ground through variable resistor 108. In addition, a 20-volt Zener diode 101 serves as a regulator for the'collector supply of the V transistor 100.

The operation of the kv. regulator may best be understood by assuming an increase in the amplitude of voltage wave (g), this being the output of the filter 88 which supplies the X-ray transformer 90. With an increase in this output voltage, the feedback voltage on conductor 92 also increases and the rectified D.C. output voltage from diode- 96 increases to a point where Zener diode 104 begins to conduct. Conductionthrough the Zener diode causes the transistor 100 to begin conducting a portion of the D.C.

voltage to ground. This causes a decrease in the con-' trol voltage being applied to the sawtooth oscillator, including the unijunction transistor 57. A decrease in this control voltage causes an increase in the output frequency from the sawtooth oscillator and -a corresponding increase in frequency of the control impulses (b) applied I transistor to begin conducting. The collector-emitter then and 126 and to ground through the thermal cutout 134 of conductor B. This introduces still another phaseireversal, so that the collector-emitter circuit of transistor 72 r is in the normally closed position and thereby shunts the square wave (e) to'ground, thus maintaining the emitter circuitin the off position. It will also be noted thatthe green light 136 is connected directly from the negative potential of conductor C to ground and is therefore burngfi V Toroperate the X-ray, switch is of discharge being dependent upon the RC time constant of the series circuit including capacitor 112 and resistors 128 and 130. The discharge current from capacitor 112 is the reverse of the charging current and is thereby blocked by diode 118 which isolates the base of the transistor 122 from the capacitor timing circuit. The base of the switching transistor'122 is now looking into When the load side of the switching transistor opens, the square wave (e) is no longer shunted to ground.,The square wave 15 applied once more to the inverter shown in FIGURE 1 and the X-ray anode transformer '90 is energized in the manner previously described. The output 7 from the reactor 88 is also connected through resistor 140 i to the red hght 132 which indicates that the X-ray is operating. This condition of'the circuitry remains so long as the capacitor 112 is discharging. As soon' asthe capacitor 112 is fully discharged, it once again presents an open circuit to the D.C. current and thereby re-establishesthe' emitter-base circuit of transistor 122, causing the X-ray circuitry to return to its original condition.

The duration of the X-ray exposure will be seen to depend on the discharge time of the timing capacitor 112 and this, in turn, is a function of the RC time constant of pushed into the down position and held. This grounds the negatively'po-- larized plate of capacitor112 through contact 116. .The capacitor 112 immediately begins to discharge, the rate V the circuit. Thisis adjusted by means of the time setting r'heostat 130 which may be controlled froma dial calibrated in terms of time periods. It should. also be noted that, as a safety feature, the X-ray tube will not remain energized if the switch 110. does not remain depressed.

Tube head construction One of the objects of this invention, as previously set forth, is to provide a portable X-ray apparatus which is highly resistant to mechanical shock. This is of extreme importance in portable X-ray units, particularly where the unit it to be used for diagnostic or other medical purposes. The construction of the tube head of this invention by means ofwhich this objectis achieved is illustrated in FIGURES 59.'

A cylindrical outer metallic shell 150 is provided having a closed end 152 and an open end 154. The open end 154 of the shell is closed by' the circular cap 156 of the inner assembly which is, removable from the shell. The side of the'shell includes an opening having a plastic window 158 for the transmission of X-ray generated by the X-ray tube 55. The open end 154 of the cylindrical shell also includes an annular shoulder 160 upon which the end cap 156 may rest. The closed end 152 of the shell also carries a pair of alignment pins 162 for proper alignment of the inner assembly when it is inserted into the shell.

The inner assembly of the tube head comprises three stringers 164, 166 and 168 which extend the length of the assembly and are bolted at their left ends to the end cap 156 and at their right ends to the casting 170 which forms the base of transformer 90. Thus the transformer casting 170 serves a dual function as a portion of the transformer and also as the end of the inner assembly. Also, the base of the transformer casting 170 includes recesses 172 for receiving alignment pins 162.

It will be noted that the stringer 164 is actually in two parts, a left hand portion 164a and a right hand portion 164b, as is illustrated in FIGURE 5. However, this is solely for purposes of clearance. Within the stringers 164, 166 and 168 and essentially at the center of the cylindrical shell 150 there is mounted a cast aluminum thermal radiator 174 which is shaped to somewhat resemble a gear wheel. The hub of the radiator receives the anode end 176 of the X-ray tube 55 and includes a set screw 178 for securingthe tube in position. The'outer periphery of the radiator is grooved as illustrated most clearly in FIG- URE 8 to provide increased heat radiation surface.

The radiator 174 is mounted within the stringers by means of neoprene cylinders 180, each mounted between a bracket 182 on a stringer and a bracket 184 mounted on the radiator 174 in one of the three openings provided therein, as illustrated in FIGURE 8. The neoprene cylinders act as shock mounts for the radiator and for the end of the X-ray tube 55. The ends of the neoprene shock mounts are bridged by means of metallic straps 186 which prevent capacitive build-up of voltages between the tube brackets. The left end of the X-ray tube 55 is left unsecured. The end cap 156 of the inner assembly includes the necessary operating instruments and electrical connectors, as illustrated in FIGURE 7.

It may be seen that the mass of the radiator 174 performs two useful functions. First it tends to act as a heat sink that absorbs the waste heat. Secondly, because of the resilient mountings it will tend to reduce any impacts or shocks on the tube.

In keeping with the lightness and portability requirements of this invention, the tube head is filled with a gas, sulfur hexafiuoride, for example, rather than an oil. Accordingly, the end cap 156 includes a pressure gauge 188, a charging valve 190 and a thermal blow-out safety plug 192 as well as the electrical connector 193.

It is, of course, necessary that electrical connections be made between the transformer 90 and the electrical connector 193 on the cathode end of the inner assembly. However, it is also important that the necessary conduc- 6 tors'be-kept as far as possible from the high voltages utilized in the'X-ray tube 55. This is achieved in the present invention by use of a flexible plastic insulating strip 194 which may be of-a material such as Plexiglas having a high degree of resiliency. The strip is placed with its ends against the transformer casting 170 and the inner side of end cap 156. The required conductors 196 are secured to the strip by any suitable means, such as wrapping with twine. 7

As will be noted from the illustration of FIGURE 6, strip 194 is longer than the straight line distance between the casting 170 and the cap 156 so that it bows outwardly holding the wires away from the remainder of the tube head structure. When the inner assembly is placed into the. cylindrical shell, the plastic strip 194 is easily bowed inwardly so as to clear the. annular shoulder but then springs outwardly against the shell.150 as soon as the inner assembly is in place. This provides positive displacement of the conductors .196 as far aspossible from the high voltage portionsof the structure. The inner assembly is retainedwithin the cylindrical shell by means of a retaining ring 198 which seats in a groove 200.

An additional and unobvious feature of this invention resides in the fact that certain high frequencies, including the 400 cycle employed herein, creates an audible signal when applied to the tube head assembly. The aural alarm so created serves an important function as a warning signal that X-rays are being produced.

It will be apparent to those skilled in the art that the apparatus of this invention provides a number of features for achieving light-weight, portable, reliable X-ray equipment. It will also be recognized that the apparatus of this invention may be subject to a number of variations and modifications without departing from its spirit and scope. Accordingly, it is to be understood that the foregoing specification is illustrative only, rather than limiting. The invention is limited only by the scope of the following claims.

What is claimed:

1. An X-ray apparatus including the combination of:

an X-ray tube having a cathode and a high voltage anode,

a battery power supply effective to provide a direct current,

Variable frequency converter means coupled to the power supply, said converter means being effective to convert the direct current from said supply into an alternating current,

an anode transformer having a primary and a secondary, said secondary being coupled to the high voltage anode of said X-ray tube, and

frequency responsive means coupling the primary of the anode transformer to the converter means, said frequency responsive means being effective to supply a voltage to the primary that is a function of the frequency.

2. The combination of claim 1 including: a

means for varying the frequency of the alternating current whereby the voltage supplied to the primary is varied.

3. The combination of claim 1 including:

feed back means coupled to the converter means and responsive to the voltage coupled to the primary, said feedback means being effective to vary the frequency of the converter means so as to maintain the voltage on the primary constant.

4. The combination of claim 1 wherein the:

converter means is responsive to a control voltage so as to vary the frequency of the alternating current, as

' a function of the control voltage, and

feedback means responsive to the voltage supplied to said transformer by said converter to provide a control voltage that is a function thereof, said feedback means being coupled to the converter to supply the control voltage thereto whereby the frequency of the current is varied to maintain the voltage on the anode constant. V

5. An X-ray apparatus including the combination of:

an X-ray tube having a cathode and a high voltage anode, I I

a source of direct current, 7

variable frequency converter means coupled to said source, said converter means being responsive to a control voltage and effective to convert the direct current into an alternating current having a frequency that is a function of the control voltage,

an anode transformer having a primary and a secondary,

frequency responsive means coupling the primary of the anode transformer to the converter means, said frequency responsive means being effective to supply a voltage to the primary that is a function of the frequency,

feedback means coupled to the frequency responsive means to produce a control voltage proportional to the voltage in the transformer, said feedback means constant, and

means coupling the secondary of anodes.

References Cited UNITED sTATEs PATENTS Sweeny et' al. 250-95 Boucher 25090 Bross 25()-102 X Johnson 307-885 X Drenck 250-103 Jones 307--88.5 X Ohde et a1 250-102 X WILLIAM F. LINDQUIST, Primary Examiner. ARCHIE R. BORCHELT, RALPH G. NILSON,

Examiners. a

the transformer to the

Claims (1)

1. AN X-RAY APPARATUS INCLUDING THE COMBINATION OF: AN X-RAY TUBE HAVING A CATHODE AND A HIGH VOLTAGE ANODE, A BATTERY POWER SUPPLY EFFECTIVE TO PROVIDE A DIRECT CURRENT, VARIABLE FREQUENCY CONVERTER MEANS COUPLED TO THE POWER SUPPLY, SAID CONVERTER MEANS BEING EFFECTIVE TO CONVERT THE DIRECT CURRENT FROM SAID SUPPLY INTO AN ALTERNATING CURRENT,

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